Introduction to Programming CS201 book HANDOUTS in pdf

<b><span style="font-size: large;">Introduction to Programming CS201 book HANDOUTS in pdf</span></b><div> <br /></div> <div> <span style="background-color: white; color: #aaaaaa; font-family: "Open Sans", Arial, "Helvetice Neue", sans-serif; font-size: 18px; text-align: center;">Handouts | Lectures | Contents | Books</span></div> <div> <span style="background-color: white; color: #aaaaaa; font-family: "Open Sans", Arial, "Helvetice Neue", sans-serif; font-size: 18px; text-align: center;"><br /></span></div> <div> <span style="background-color: white; color: #aaaaaa; font-family: "Open Sans", Arial, "Helvetice Neue", sans-serif; font-size: 18px; text-align: center;"><br /></span></div> <div> <span style="background-color: white; color: #aaaaaa; font-family: "Open Sans", Arial, "Helvetice Neue", sans-serif; font-size: 18px; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjosZOVvYUDDz2YuX7WiomRAyaoFhoow65vMDBL6hdqfxp5n6mp5ymzZtyTUHR2jNp-W1PloQcaHkWpW61c08rJkGGY7djfoSc3iEiK1DhZsBf4cyhz58TevlMH4wTXqSMpWUUVvAV6pGw/s1600/CS%252B201-%252BIntroduction%252BTo%252BProgramming%252BWith%252BJava.jpg" imageanchor="1"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjosZOVvYUDDz2YuX7WiomRAyaoFhoow65vMDBL6hdqfxp5n6mp5ymzZtyTUHR2jNp-W1PloQcaHkWpW61c08rJkGGY7djfoSc3iEiK1DhZsBf4cyhz58TevlMH4wTXqSMpWUUVvAV6pGw/s1600/CS%252B201-%252BIntroduction%252BTo%252BProgramming%252BWith%252BJava.jpg" /></a></span></div> <div> <span style="background-color: white; color: #aaaaaa; font-family: "Open Sans", Arial, "Helvetice Neue", sans-serif; font-size: 18px; text-align: center;"><br /></span></div> <div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 3</div> <div> Lecture No. 1</div> <div> Summary</div> <div> o What is programming</div> <div> o Why programming is important</div> <div> o What skills are needed</div> <div> o Develop a basic recipe for writing programs</div> <div> o Points to remember</div> <div> What is programming</div> <div> As this course is titled “Introduction to programming”, therefore it is most essential</div> <div> and appropriate to understand what programming really means. Let us first see a</div> <div> widely known definition of programming.</div> <div> Definition: "A program is a precise sequence of steps to solve a particular problem.”</div> <div> It means that when we say that we have a program, it actually means that we know</div> <div> about a complete set activities to be performed in a particular order. The purpose of</div> <div> these activities is to solve a given problem.</div> <div> Alan Perlis, a professor at Yale University, says:</div> <div> "It goes against the grain of modern education to teach children to program. What fun</div> <div> is there in making plans, acquiring discipline in organizing thoughts, devoting</div> <div> attention to detail and learning to be self-critical? "</div> <div> It is a sarcastic statement about modern education, and it means that the modern</div> <div> education is not developing critical skills like planning, organizing and paying</div> <div> attention to detail. Practically, in our day to day lives we are constantly planning,</div> <div> organizing and paying attention to fine details (if we want our plans to succeed). And</div> <div> it is also fun to do these activities. For example, for a picnic trip we plan where to go,</div> <div> what to wear, what to take for lunch, organize travel details and have a good time</div> <div> while doing so.</div> <div> When we talk about computer programming then as Mr. Steve Summit puts it</div> <div> “At its most basic level, programming a computer simply means telling it what to do,</div> <div> and this vapid-sounding definition is not even a joke. There are no other truly</div> <div> fundamental aspects of computer programming; everything else we talk about will</div> <div> simply be the details of a particular, usually artificial, mechanism for telling a</div> <div> computer what to do. Sometimes these mechanisms are chosen because they have</div> <div> been found to be convenient for programmers (people) to use; other times they have</div> <div> been chosen because they're easy for the computer to understand. The first hard thing</div> <div> about programming is to learn, become comfortable with, and accept these artificial</div> <div> mechanisms, whether they make ``sense'' to you or not. “</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 4</div> <div> Why Programming is important</div> <div> The question most of the people ask is why should we learn to program when there</div> <div> are so many application software and code generators available to do the task for us.</div> <div> Well the answer is as give by the Matthias Felleisen in the book ‘How to design</div> <div> programs’</div> <div> “The answer consists of two parts. First, it is indeed true that traditional forms of</div> <div> programming are useful for just a few people. But, programming as we the authors</div> <div> understand it is useful for everyone: the administrative secretary who uses</div> <div> spreadsheets as well as the high-tech programmer. In other words, we have a broader</div> <div> notion of programming in mind than the traditional one. We explain our notion in a</div> <div> moment. Second, we teach our idea of programming with a technology that is based</div> <div> on the principle of minimal intrusion. Hence, our notion of programming teaches</div> <div> problem-analysis and problem-solving skills without imposing the overhead of</div> <div> traditional programming notations and tools.”</div> <div> Hence learning to program is important because it develops analytical and problem</div> <div> solving abilities. It is a creative activity and provides us a mean to express abstract</div> <div> ideas. Thus programming is fun and is much more than a vocational skill. By</div> <div> designing programs, we learn many skills that are important for all professions. These</div> <div> skills can be summarized as:</div> <div> o Critical reading</div> <div> o Analytical thinking</div> <div> o Creative synthesis</div> <div> What skills are needed</div> <div> Programming is an important activity as people life and living depends on the</div> <div> programs one make. Hence while programming one should</div> <div> o Paying attention to detail</div> <div> o Think about the reusability.</div> <div> o Think about user interface</div> <div> o Understand the fact the computers are stupid</div> <div> o Comment the code liberally</div> <div> Paying attention to detail</div> <div> In programming, the details matter. This is a very important skill. A good programmer</div> <div> always analyzes the problem statement very carefully and in detail. You should pay</div> <div> attention to all the aspects of the problem. You can't be vague. You can't describe</div> <div> your program 3/4th of the way, then say, "You know what I mean?'', and have the</div> <div> compiler figure out the rest.</div> <div> Furthermore you should pay attention to the calculations involved in the program, its</div> <div> flow, and most importantly, the logic of the program. Sometimes, a grammatically</div> <div> correct sentence does not make any sense. For example, here is a verse from poem</div> <div> "Through the Looking Glass" written by Lewis Carol:</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 5</div> <div> “Twas brillig, and the slithy toves</div> <div> Did gyre and gimble in the wabe “</div> <div> The grammar is correct but there is no meaning. Similarly, the sentence, "Mr. ABC</div> <div> sleeps thirty hours every day", is grammatically correct but it is illogical.</div> <div> So it may happen that a program is grammatically correct. It compiles and runs but</div> <div> produces incorrect or absurd results and does not solve the problem. It is very</div> <div> important to pay attention to the logic of the program.</div> <div> Think about the reusability</div> <div> When ever you are writing a program, always keep in mind that it could be reused at</div> <div> some other time. Also, try to write in a way that it can be used to solve some other</div> <div> related problem. A classic example of this is:</div> <div> Suppose we have to calculate the area of a given circle. We know the area of a circle</div> <div> is (Pi * r2). Now we have written a program which calculates the area of a circle with</div> <div> given radius. At some later time we are given a problem to find out the area of a ring.</div> <div> The area of the ring can be calculated by subtracting the area of outer circle from the</div> <div> area of the inner circle. Hence we can use the program that calculates the area of a</div> <div> circle to calculate the area of the ring.</div> <div> Think about Good user interface</div> <div> As programmers, we assume that computer users know a lot of things, this is a big</div> <div> mistake. So never assume that the user of your program is computer literate. Always</div> <div> provide an easy to understand and easy to use interface that is self explanatory.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 6</div> <div> Understand the fact that computers are stupid</div> <div> Computers are incredibly stupid. They do exactly what you tell them to do: no more,</div> <div> no less-- unlike human beings. Computers can't think by themselves. In this sense,</div> <div> they differ from human beings. For example, if someone asks you, “What is the</div> <div> time?”, “Time please?” or just, “Time?” you understand anyway that he is asking the</div> <div> time but computer is different. Instructions to the computer should be explicitly</div> <div> stated. Computer will tell you the time only if you ask it in the way you have</div> <div> programmed it.</div> <div> When you're programming, it helps to be able to "think'' as stupidly as the computer</div> <div> does, so that you are in the right frame of mind for specifying everything in minute</div> <div> detail, and not assuming that the right thing will happen by itself.</div> <div> Comment the code liberally</div> <div> Always comment the code liberally. The comment statements do not affect the</div> <div> performance of the program as these are ignored by the compiler and do not take any</div> <div> memory in the computer. Comments are used to explain the functioning of the</div> <div> programs. It helps the other programmers as well as the creator of the program to</div> <div> understand the code.</div> <div> Program design recipe</div> <div> In order to design a program effectively and properly we must have a recipe to follow.</div> <div> In the book name ‘How to design programs’ by Matthias Felleisen.and the co-worker,</div> <div> the idea of design recipe has been stated very elegenlty as</div> <div> “Learning to design programs is like learning to play soccer. A player must learn to</div> <div> trap a ball, to dribble with a ball, to pass, and to shoot a ball. Once the player knows</div> <div> those basic skills, the next goals are to learn to play a position, to play certain</div> <div> strategies, to choose among feasible strategies, and, on occasion, to create variations</div> <div> of a strategy because none fits. “</div> <div> The author then continue to say that:</div> <div> “A programmer is also very much like an architect, a composers, or a writer. They are</div> <div> creative people who start with ideas in their heads and blank pieces of paper. They</div> <div> conceive of an idea, form a mental outline, and refine it on paper until their writings</div> <div> reflect their mental image as much as possible. As they bring their ideas to paper, they</div> <div> employ basic drawing, writing, and playing music to express certain style elements of</div> <div> a building, to describe a person's character, or to formulate portions of a melody. They</div> <div> can practice their trade because they have honed their basic skills for a long time and</div> <div> can use them on an instinctive level.</div> <div> Programmers also form outlines, translate them into first designs, and iteratively</div> <div> refine them until they truly match the initial idea. Indeed, the best programmers edit</div> <div> and rewrite their programs many times until they meet certain aesthetic standards.</div> <div> And just like soccer players, architects, composers, or writers, programmers must</div> <div> practice the basic skills of their trade for a long time before they can be truly creative.</div> <div> Design recipes are the equivalent of soccer ball handling techniques, writing</div> <div> techniques, arrangements, and drawing skills. “</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 7</div> <div> Hence to design a program properly, we must:</div> <div> o Analyze a problem statement, typically expressed as a word problem.</div> <div> o Express its essence, abstractly and with examples.</div> <div> o Formulate statements and comments in a precise language.</div> <div> o Evaluate and revise the activities in light of checks and tests and</div> <div> o Pay attention to detail.</div> <div> All of these are activities that are useful, not only for a programmer but also for a</div> <div> businessman, a lawyer, a journalist, a scientist, an engineer, and many others.</div> <div> Let us take an example to demonstrate the use of design recipe:</div> <div> Suppose we have to develop a payroll system of a company. The company has</div> <div> permanent staff, contractual staff, hourly based employees and per unit making</div> <div> employees. Moreover, there are different deductions and benefits for permanent</div> <div> employees and there is a bonus for per unit making employees and overtime for</div> <div> contractual employees.</div> <div> We need to analyze the above problem statement. The company has four categories of</div> <div> employees; i.e.; Permanent staff, Contractual staff, hourly based employees and per</div> <div> unit making employees. Further, permanent staff has benefits and deductions</div> <div> depending upon their designation. Bonus will be given to per unit making employees</div> <div> if they make more than 10 pieces a day. Contractual employee will get overtime if</div> <div> they stay after office hours.</div> </div> <div> <br /></div> <div> <div> Now divide the problem into small segments and calculations. Also include examples</div> <div> in all segments. In this problem, we should take an employee with his details from</div> <div> each category. Let’s say, Mr. Ahmad is a permanent employee working as Finance</div> <div> Manager. His salary is Rs.20000 and benefits of medical, car allowance and house</div> <div> rent are Rs.4000 and there is a deduction of Rs.1200. Similarly, we should consider</div> <div> employees from other categories. This will help us in checking and testing the</div> <div> program later on.</div> <div> The next step is to formulate these statements in a precise language, i.e. we can use</div> <div> the pseudo code and flowcharting. which will be then used to develop the program</div> <div> using computer language.</div> <div> Then the program should be evaluated by testing and checking. If there are some</div> <div> changes identified, we revise the activities and repeat the process. Thus repeating the</div> <div> cycle, we achieve a refined solution.</div> <div> Points to remember</div> <div> Hence the major points to keep in mind are:</div> <div> o Don’t assume on the part of the users</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 8</div> <div> o User Interface should be friendly</div> <div> o Don’t forget to comment the code</div> <div> o PAY ATTENTION TO DETAIL</div> <div> o Program, program and program, not just writing code, but the whole</div> <div> process of design and development</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 9</div> <div> Lecture No. 2</div> <div> Reading Material</div> <div> Deitel & Deitel – C++ How to Program chapter 1</div> <div> 1.2, 1.3, 1.4, 1.6,</div> <div> 1.7</div> <div> 1.11, 1.12, 1.13</div> <div> Summary</div> <div> o Software Categories</div> <div> o System Software</div> <div> o Application Software</div> <div> o History of C language</div> <div> o Development Environment of ‘C’</div> <div> Software Categories</div> <div> Software is categorized into two main categories</div> <div> o System Software</div> <div> o Application Software</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 10</div> <div> System Software</div> <div> The system software controls the computer. It communicates with computer’s</div> <div> hardware (key board, mouse, modem, sound card etc) and controls different aspects of</div> <div> operations. Sub categories of system software are:</div> <div> o Operating system</div> <div> o Device drivers</div> <div> o Utilities</div> <div> Operating system</div> <div> An operating system (sometimes abbreviated as "OS") is the program that manages all</div> <div> the other programs in a computer. It is a integrated collection of routines that service</div> <div> the sequencing and processing of programs by a computer. Note: An operating system</div> <div> may provide many services, such as resource allocation, scheduling, input/output</div> <div> control, and data management.</div> <div> Definition</div> <div> “Operating system is the software responsible for controlling the allocation and usage of hardware</div> <div> resources such as memory, central processing unit (CPU) time, disk space, and peripheral devices. The</div> <div> operating system is the foundation on which applications, such as word processing and spreadsheet</div> <div> programs, are built. (Microsoft)”</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 11</div> <div> Device drivers</div> <div> The device driver software is used to communicate between the devices and the</div> <div> computer. We have monitor, keyboard and mouse attached to almost all PC’s; if we</div> <div> look at the properties of these devices we will see that the operating system has</div> <div> installed special software to control these devices. This piece of software is called</div> <div> device driver software. When we attach a new device with the computer, we need</div> <div> software to communicate with this device. These kinds of software are known as</div> <div> device drivers e.g. CD Rom driver, Sound Card driver and Modem driver. Normally</div> <div> manufacturer of the device provide the device driver software with the device. For</div> <div> scanners to work properly with the computers we install the device driver of the</div> <div> scanner. Nowadays if you have seen a scanner, it comes with TWAIN Drivers.</div> <div> TWAIN stands for Technology Without An Interesting Name.</div> <div> Utility Software</div> <div> Utility software is a program that performs a very specific task, usually related to</div> <div> managing system resources. You would have noticed a utility of Disk Compression.</div> <div> Whenever you write a file and save it to the disk, Compression Utility compresses the</div> <div> file (reduce the file size) and write it to the disk and when you request this file from</div> <div> the disk, the compression utility uncompressed the file and shows its contents.</div> <div> Similarly there is another utility, Disk Defragmentation which is used to defragment</div> <div> the disk. The data is stored on the disks in chunks, so if we are using several files and</div> <div> are making changes to these files then the different portions of file are saved on</div> <div> different locations on the disk. These chunks are linked and the operating system</div> <div> knows how to read the contents of file from the disk combining all the chunks.</div> <div> Similarly when we delete a file then the place where that file was stored on the disk is</div> <div> emptied and is available now to store other files. As the time goes on, we have a lot of</div> <div> empty and used pieces on the disk. In such situation we say that the disk is</div> <div> fragmented now. If we remove this fragmentation the chunks of data on the disk will</div> <div> be stored close to each other and thus reading of data will be faster. For the purpose of</div> <div> removing fragmentation on the disk the Defragmentation utility is used.</div> <div> The compilers and interpreters also belong to the System Software category.</div> <div> Application software</div> <div> A program or group of programs designed for end users. For example a program for</div> <div> Accounting, Payroll, Inventory Control System, and guided system for planes. GPS</div> <div> (global positioning system), another application software, is being used in vehicles,</div> <div> which through satellite determines the geographical position of the vehicle</div> <div> History of C language</div> <div> The C language was developed in late 60’s and early 70’s, in Bell Laboratories. In</div> <div> those days BCPL and B languages were developed there. The BCPL language was</div> <div> developed in 1967 by Martin Richards as a language for writing operating systems</div> <div> software and compilers. In 1970 Ken Thompson used B language to create early</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 12</div> <div> versions of the UNIX operating system at Bell Laboratories. Thus both the languages</div> <div> were being used to develop various system software even compilers. Both BCPL and</div> <div> B were ‘type less’ languages, every data item occupied one ‘word’ in memory and the</div> <div> burden of treating a data item as a whole number or real number, for example was the</div> <div> responsibility of the programmer.</div> <div> Dennis Ritchie developed a general purpose language, called C language, by using</div> <div> different features of BCPL and B languages. C uses many important concepts of</div> <div> BCPL and B while adding data typing and other features. In the start C became</div> <div> widely known as the development language of the UNIX operating system, and the</div> <div> UNIX operating system was written by using this C language. The C language is so</div> <div> powerful that the compiler of C and other various operating systems are written in C.</div> <div> C language has almost unlimited powers to do with computers. You can program to</div> <div> turn on or off any device of computer. You can do a lot to hard disk and other</div> <div> peripherals. It is very easy to write a program in C that stops the running of computer.</div> <div> So be careful while programming in C.</div> <div> The C language and UNIX operating system widely spread in educational and</div> <div> research institutions. There was C and UNIX everywhere. Due to the wide spread of</div> <div> C, different researchers started to add their features in the language. And thus</div> <div> different variations in C came into existence. Many universities developed their own</div> <div> C by adding different features to the C language developed by Ritchie. These</div> <div> variations led to the need of a standard version of C. In 1983 a technical committee</div> <div> was created under the American National Standards Committee on Computer and</div> <div> Information Processing to provide an unambiguous and machine-independent</div> <div> definition of the language. In 1989 the standard was approved. ANSI cooperated with</div> <div> the International Standard Organization (ISO) to standardize C worldwide.</div> <div> Tools of the trade</div> <div> As programmer we need different tools to develop a program. These tools are needed</div> <div> for the life cycle of programs</div> <div> Editors</div> <div> First of all we need a tool for writing the code of a program. For this purpose we used</div> <div> Editors in which we write our code. We can use word processor too for this, but word</div> <div> processors have many other features like bold the text, italic, coloring the text etc, so</div> <div> when we save a file written in a word processor, lot of other information including the</div> <div> text is saved on the disk. For programming purposes we don’t need these things we</div> <div> only need simple text. Text editors are such editors which save only the text which we</div> <div> type. So for programming we will be using a text editor</div> <div> Compiler and Interpreter</div> <div> As we write the code in English and we know that computers can understand only 0s</div> <div> and 1s. So we need a translator which translates the code of our program into machine</div> <div> language. There are two kinds of translators which are known as Interpreter and</div> <div> Compilers. These translators translate our program which is written in C-Language</div> <div> into Machine language. Interpreters translates the program line by line meaning it</div> <div> reads one line of program and translates it, then it reads second line, translate it and so</div> <div> on. The benefit of it is that we get the errors as we go along and it is very easy to</div> <div> correct the errors. The drawback of the interpreter is that the program executes slowly</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 13</div> <div> as the interpreter translates the program line by line. Another drawback is that as</div> <div> interpreters are reading the program line by line so they cannot get the overall picture</div> <div> of the program hence cannot optimize the program making it efficient.</div> <div> Compilers also translate the English like language (Code written in C) into a language</div> <div> (Machine language) which computers can understand. The Compiler read the whole</div> <div> program and translates it into machine language completely. The difference between</div> <div> interpreter and compiler is that compiler will stop translating if it finds an error and</div> <div> there will be no executable code generated whereas Interpreter will execute all the</div> <div> lines before error and will stop at the line which contains the error. So Compiler needs</div> <div> syntactically correct program to produce an executable code. We will be using</div> <div> compiler in our course</div> <div> Debugger</div> <div> Another important tool is Debugger. Every programmer should be familiar with it.</div> <div> Debugger is used to debug the program i.e. to correct the logical errors. Using</div> <div> debugger we can control our program while it is running. We can stop the execution</div> <div> of our program at some point and can check the values in different variables, can</div> <div> change these values etc. In this way we can trace the logical errors in our program and</div> <div> can see whether our program is producing the correct results. This tool is very</div> <div> powerful, so it is complex too</div> <div> Linker</div> <div> Most of the time our program is using different routines and functions that are located</div> <div> in different files, hence it needs the executable code of those routines/functions.</div> <div> Linker is a tool which performs this job, it checks our program and includes all those</div> <div> routines or functions which we are using in our program to make a standalone</div> <div> executable code and this process is called Linking</div> <div> Loader</div> <div> After a executable program is linked and saved on the disk and it is ready for</div> <div> execution. We need another process which loads the program into memory and then</div> <div> instruct the processor to start the execution of the program from the first instruction</div> <div> (the starting point of every C program is from the main function). This processor is</div> <div> known as loader. Linker and loaders are the part of development environment. These</div> <div> are part of system software.</div> <div> The following figure represents a graphical explanation of all the steps involved in</div> <div> writing and executing a program.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 14</div> <div> Preprocessor program</div> <div> processes the code.</div> <div> Loader puts program</div> <div> in memory.</div> <div> CPU takes each</div> <div> instruction and</div> <div> executes it, possibly</div> <div> storing new data</div> <div> values as the</div> <div> program executes.</div> <div> Compiler creates object</div> <div> code and stores</div> <div> it on disk.</div> <div> Linker links the object</div> <div> code with the libraries</div> <div> Loader</div> <div> Primary Memory</div> <div> Compiler</div> <div> Editor</div> <div> Preprocessor</div> <div> Linker</div> <div> Primary Memory</div> <div> ...</div> <div> ...</div> <div> ...</div> <div> ...</div> <div> Disk</div> <div> Disk</div> <div> Disk</div> <div> CPU</div> <div> Disk</div> <div> Disk</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 15</div> <div> Lecture No. 3</div> <div> Reading Material</div> <div> Deitel & Deitel – C++ How to Program chapter 1</div> <div> 1.19, 1.20, 1.21,</div> <div> 1.22</div> <div> Summary</div> <div> First C program</div> <div> Variables</div> <div> Data Types</div> <div> Arithmetic Operators</div> <div> Precedence of Operators</div> <div> Tips</div> <div> First C program</div> <div> The best way to learn C is to start coding right away. So here is our very first program</div> <div> in C.</div> <div> # include <iostream.h></div> <div> main()</div> <div> {</div> <div> cout << "Welcome to Virtual University of Pakistan";</div> <div> }</div> <div> We will look at this code line by line and try to understand them.</div> <div> # include <iostream.h></div> <div> #include: This is a pre-processor directive. It is not part of our program; it is an</div> <div> instruction to the compiler. It tells the C compiler to include the contents of a file, in</div> <div> this case the system file iostream.h. The compiler knows that it is a system file, and</div> <div> therefore looks for it in a special place. The features of preprocessor will be discussed</div> <div> later. For the time being take this line on faith. You have to write this line. The sign #</div> <div> is known as HASH and also called SHARP.</div> <div> <iostream.h></div> <div> This is the name of the library definition file for all Input Output Streams. Your</div> <div> program will almost certainly want to send stuff to the screen and read things from the</div> <div> keyboard. iostream.h is the name of the file in which has code to do that work for you</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 16</div> <div> main()</div> <div> The name main is special, in that the main is actually the one which is run when your</div> <div> program is used. A C program is made up of a large number of functions. Each of</div> <div> these is given a name by the programmer and they refer to each other as the program</div> <div> runs. C regards the name "main" as a special case and will run this function first. If</div> <div> you forget to have a main function, or mistype the name, the compiler will give you</div> <div> an error.</div> <div> Notice that there are parentheses (“( )”, normal brackets) with main. Here the</div> <div> parentheses contain nothing. There may be something written inside the parentheses.</div> <div> It will be discussed in next lectures.</div> <div> { }</div> <div> Next, there is a curly bracket also called braces("{ }"). For every open brace there</div> <div> must be a matching close. Braces allows to group together pieces of a program. The</div> <div> body of main is enclosed in braces. Braces are very important in C; they enclose the</div> <div> blocks of the program.</div> <div> cout << “ Welcome to Virtual University of Pakistan”</div> <div> cout:</div> <div> This is known as out put stream in C and C++. Stream is a complicated thing, you will</div> <div> learn about it later. Think a stream as a door. The data is transferred through stream,</div> <div> cout takes data from computer and sends it to the output. For the moment it is a</div> <div> screen of the monitor. hence we use cout for output.</div> <div> <<</div> <div> The sign << indicates the direction of data. Here it is towards cout and the function of</div> <div> cout is to show data on the screen.</div> <div> “ Welcome to Virtual University of Pakistan”</div> <div> The thing between the double quotes (“ ”) is known as character string. In C</div> <div> programming character strings are written in double quotes. Whatever is written after</div> <div> << and within quotation marks will be direct it to cout, cout will display it on the</div> <div> screen.</div> <div> ;</div> <div> There is a semicolon (;) at the end of the above statement. This is very important. All</div> <div> C statements end with semicolon (;). Missing of a semicolon (;) at the end of</div> <div> statement is a syntax error and compiler will report an error during compilation. If</div> <div> there is only a semicolon (;) on a line than it will be called a null statement. i.e. it does</div> <div> nothing. The extra semicolons may be put at the end but are useless and aimless. Do</div> <div> not put semicolon (;) at a wrong place, it may cause a problem during the execution of</div> <div> the program or may cause a logical error.</div> <div> In this program we give a fixed character string to cout and the program prints it to</div> <div> the screen as:</div> <div> Variables</div> <div> During programming we need to store data. This data is stored in variables. Variables</div> <div> are locations in memory for storing data. The memory is divided into blocks. It can be</div> <div> viewed as pigeon-holes. You can also think of it as PO Boxes. In post offices there are</div> <div> different boxes and each has an address. Similarly in memory, there is a numerical</div> <div> address for each location of memory (block). It is difficult for us to handle these</div> <div> numerical addresses in our programs. So we give a name to these locations. These</div> <div> names are variables. We call them variables because they can contain different values</div> <div> at different times.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 17</div> <div> The variable names in C may be started with a character or an underscore ( _ ). But</div> <div> avoid starting a name with underscore ( _ ). C has many libraries which contain</div> <div> variables and function names normally starting with underscore ( _ ). So your variable</div> <div> name starting with underscore ( _ ) may conflict with these variables or function</div> <div> names.</div> <div> In a program every variable has</div> <div> Name</div> <div> Type</div> <div> Size</div> <div> Value</div> <div> The variables having a name, type and size (type and size will be discussed later) are</div> <div> just empty boxes. They are useless until we put some value in them. To put some</div> <div> value in these boxes is known as assigning values to variables. In C language, we use</div> <div> assignment operator for this purpose.</div> <div> Assignment Operator</div> <div> In C language equal-to-sign (=) is used as assignment operator. Do not confuse the</div> <div> algebraic equal-to with the assignment operator. In Algebra X = 2 means the value of</div> <div> X is 2, whereas in C language X = 2 (where X is a variable name) means take the</div> <div> value 2 and put it in the memory location labeled as X, afterwards you can assign</div> <div> some other value to X, for example you can write X = 10, that means now the</div> <div> memory location X contains the value 10 and the previous value 2 is no more there.</div> <div> Assignment operator is a binary operator (a binary operator has two operands). It must</div> <div> have variable on left hand side and expression (that evaluates to a single value) on</div> <div> right hand side. This operator takes the value on right hand side and stores it to the</div> <div> location labeled as the variable on left hand side, e.g. X = 5, X = 10 + 5, and X = X</div> <div> +1.</div> <div> In C language the statement X = X + 1 means that add 1 to the value of X and then</div> <div> store the result in X variable. If the value of X is 10 then after the execution of this</div> <div> statement the value of X becomes 11. This is a common practice for incrementing the</div> <div> value of the variable by ‘one in C language. Similarly you can use the statement X =</div> <div> X - 1 for decrementing the value of the variable by one. The statement X = X + 1 in</div> <div> algebra is not valid except when X is infinity. So do not confuse assignment operator</div> <div> (=) with equal sign (=) in algebra. Remember that assignment operator must have a</div> <div> variable name on left hand side unlike algebra in which you can use expression on</div> <div> both sides of equal sign (=). For example, in algebra, X +5 = Y + 7 is correct but</div> <div> incorrect in C language. The compiler will not understand it and will give error.</div> <div> Data Types</div> <div> A variable must have a data type associated with it, for example it can have data types</div> <div> like integer, decimal numbers, characters etc. The variable of type Integer stores</div> <div> integer values and a character type variable stores character value. The primary</div> <div> difference between various data types is their size in memory. Different data types</div> <div> have different size in memory depending on the machine and compilers. These also</div> <div> affect the way they are displayed. The ‘cout’ knows how to display a digit and a</div> <div> character. There are few data types in C language. These data types are reserved</div> <div> words of C language. The reserve words can not be used as a variable name.</div> <div> Let’s take a look into different data types that the C language provides us to deal with</div> <div> whole numbers, real numbers and character data.</div> <div> Whole Numbers</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 18</div> <div> The C language provides three data types to handle whole numbers.</div> <div> int</div> <div> short</div> <div> long</div> <div> int Data Type</div> <div> The data type int is used to store whole numbers (integers). The integer type has a</div> <div> space of 4 bytes (32 bits for windows operating system) in memory. And it is</div> <div> mentioned as ‘int’ which is a reserved word of C, so we can not use it as a variable</div> <div> name.</div> <div> In programming before using any variable name we have to declare that variable with</div> <div> its data type. If we are using an integer variable named as ‘i’, we have to declare it as</div> <div> int i ;</div> <div> The above line is known as declaration statement. When we declare a variable in this</div> <div> way, it reserves some space in memory depending on the size of data type and labels</div> <div> it with the variable name. The declaration statement int i ; reserves 4 bytes of memory</div> <div> and labels it as ‘i’. This happens at the execution time.</div> <div> Sample Program 1</div> <div> Let’s consider a simple example to explain int data type. In this example we take two</div> <div> integers, add them and display the answer on the screen.</div> <div> The code of the program is written below.</div> <div> #include <iostream.h></div> <div> main()</div> <div> {</div> <div> int x;</div> <div> int y;</div> <div> int z;</div> <div> x = 5;</div> <div> y = 10;</div> <div> z = x + y;</div> <div> cout << “x = “;</div> <div> cout << x;</div> <div> cout << “ y=“;</div> <div> cout << y;</div> <div> cout << “ z = x + y = “;</div> <div> cout << z;</div> <div> }</div> <div> The first three lines declare three variables x, y and z as following.</div> <div> int x;</div> <div> int y;</div> <div> int z;</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 19</div> <div> These three declarations can also be written on one line. C provides us the comma</div> <div> separator (,). The above three lines can be written in a single line as below</div> <div> int x, y, z;</div> <div> As we know that semicolon (;) indicates the end of the statement. So we can write</div> <div> many statements on a single line. In this way we can also write the above declarations</div> <div> in the following form</div> <div> int x; int y; int z;</div> <div> For good programming practice, write a single statement on a single line.</div> <div> Now we assign values to variables x and y by using assignment operator. The lines x</div> <div> = 5; and y = 10 assign the values 5 and 10 to the variables x and y, respectively. These</div> <div> statements put the values 5 and 10 to the memory locations labeled as x and y.</div> <div> The next statement z = x + y; evaluates the expression on right hand side. It takes</div> <div> values stored in variables x and y (which are 5 and 10 respectively), adds them and by</div> <div> using the assignment operator (=), puts the value of the result, which is 15 in this case,</div> <div> to the memory location labeled as z.</div> <div> Here a thing to be noted is that the values of x and y remains the same after this</div> <div> operation. In arithmetic operations the values of variables used in expression on the</div> <div> right hand side are not affected. They remain the same. But a statement like x = x + 1;</div> <div> is an exceptional case. In this case the value of x is changed.</div> <div> The next line cout << “ x = “ ; is simple it just displays ‘ x = ‘ on the screen.</div> <div> Now we want to display the value of x after ‘x =’. For this we write the statement</div> <div> cout << x ;</div> <div> Here comes the affect of data type on cout. The previous statement cout << “x = “ ;</div> <div> has a character string after << sign and cout simply displays the string. In the</div> <div> statement cout << x; there is a variable name x. Now cout will not display ‘x’ but the</div> <div> value of x. The cout interprets that x is a variable of integer type, it goes to the</div> <div> location x in the memory and takes its value and displays it in integer form, on the</div> <div> screen. The next line cout << ”y =”; displays ‘ y = ‘ on the screen. And line cout << y;</div> <div> displays the value of y on the screen. Thus we see that when we write something in</div> <div> quotation marks it is displayed as it is but when we use a variable name it displays the</div> <div> value of the variable not name of the variable. The next two lines cout << “z = x + y =</div> <div> ”; and cout << z; are written to display ‘z = x + y = ’ and the value of z that is 15.</div> <div> Now when we execute the program after compiling, we get the following output.</div> <div> x = 5 y = 10 z = x + y = 15</div> <div> short Data type</div> <div> We noted that the integer occupies four bytes in memory. So if we have to store a</div> <div> small integer like 5, 10 or 20 four bytes would be used. The C provides another data</div> <div> type for storing small whole numbers which is called short. The size of short is two</div> <div> bytes and it can store numbers in range of -32768 to 32767. So if we are going to use</div> <div> a variable for which we know that it will not increase from 32767, for example the</div> <div> age of different people, then we use the data type short for age. We can write the</div> <div> above sample program by using short instead of int.</div> <div> /*This program uses short data type to store values */</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 20</div> <div> #include <iostream.h></div> <div> main()</div> <div> {</div> <div> short x;</div> <div> short y;</div> <div> short z;</div> <div> x = 5;</div> <div> y = 10;</div> <div> z = x + y;</div> <div> cout << “x = “;</div> <div> cout << x;</div> <div> cout << “ y=“;</div> <div> cout << y;</div> <div> cout << “ z = x + y = “;</div> <div> cout << z;</div> <div> }</div> <div> long Data Type</div> <div> On the other side if we have a very large whole number that can not be stored in an int</div> <div> then we use the data type long provided by C. So when we are going to deal with very</div> <div> big whole numbers in our program, we use long data type. We use it in program as:</div> <div> long x = 300500200;</div> <div> Real Numbers</div> <div> The C language provides two data types to deal with real numbers (numbers with</div> <div> decimal points e.g. 1.35, 735.251). The real numbers are also known as floating point</div> <div> numbers.</div> <div> float</div> <div> double</div> <div> float Data Type</div> <div> To store real numbers, float data type is used. The float data type uses four bytes to</div> <div> store a real number. Here is program that uses float data types.</div> <div> /*This program uses short data type to store values */</div> <div> #include <iostream.h></div> <div> main()</div> <div> {</div> <div> float x;</div> <div> float y;</div> <div> float z;</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 21</div> <div> x = 12.35;</div> <div> y = 25.57;</div> <div> z = x + y;</div> <div> cout << “ x = “;</div> <div> cout << x;</div> <div> cout << “ y = “;</div> <div> cout << y;</div> <div> cout << “ z = x + y = “;</div> <div> cout << z;</div> <div> }</div> <div> double Data Type</div> <div> If we need to store a large real number which cannot be store in four bytes, then we</div> <div> use double data type. Normally the size of double is twice the size of float. In</div> <div> program we use it as:</div> <div> double x = 345624.769123;</div> <div> char Data Type</div> <div> So far we have been looking on data types to store numbers, In programming we do</div> <div> need to store characters like a,b,c etc. For storing the character data C language</div> <div> provides char data type. By using char data type we can store characters in variables.</div> <div> While assigning a character value to a char type variable single quotes are used</div> <div> around the character as ‘a’.</div> <div> /* This program uses short data type to store values */</div> <div> #include <iostream.h></div> <div> main()</div> <div> {</div> <div> char x;</div> <div> x = ’a’;</div> <div> cout << “The character value in x = “;</div> <div> cout << x;</div> <div> }</div> <div> Arithmetic Operators</div> <div> In C language we have the usual arithmetic operators for addition, subtraction,</div> <div> multiplication and division. C also provides a special arithmetic operator which is</div> <div> called modulus. All these operators are binary operators which means they operate on</div> <div> two operands. So we need two values for addition, subtraction, multiplication,</div> <div> division and modulus.</div> <div> ARITHMETIC</div> <div> OPERATION</div> <div> ARITHMETIC</div> <div> OPERATOR</div> <div> ALGEBRAIC</div> <div> EXPRESSION</div> <div> C</div> <div> EXPRESSION</div> <div> Addition + x + y x + y</div> <div> Subtraction - x – y x - y</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 22</div> <div> Multiplication * Xy x * y</div> <div> Division / x ÷ y, x / y x / y</div> <div> Modulus % x mod y x % y</div> <div> Addition, subtraction and multiplication are same as we use in algebra.</div> <div> There is one thing to note in division that when we use integer division (i.e. both</div> <div> operands are integers) yields an integer result. This means that if, for example, you</div> <div> are dividing 5 by 2 (5 / 2) it will give integer result as 2 instead of actual result 2.5.</div> <div> Thus in integer division the result is truncated to the whole number, the fractional part</div> <div> (after decimal) is ignored. If we want to get the correct result, then we should use float</div> <div> data type.</div> <div> The modulus operator returns the remainder after division. This operator can only be</div> <div> used with integer operands. The expression x % y returns the remainder after x is</div> <div> divided by y. For example, the result of 5 % 2 will be 1, 23 % 5 will be 3 and 107%10</div> <div> will be 7.</div> <div> Precedence of Operators</div> <div> The arithmetic operators in an expression are evaluated according to their precedence.</div> <div> The precedence means which operator will be evaluated first and which will be</div> <div> evaluated after that and so on. In an expression, the parentheses ( ) are used to force</div> <div> the evaluation order. The operators in the parentheses ( ) are evaluated first. If there</div> <div> are nested parentheses then the inner most is evaluated first.</div> <div> The expressions are always evaluated from left to right. The operators *, / and % have</div> <div> the highest precedence after parentheses. These operators are evaluated before + and –</div> <div> operators. Thus + and – operators has the lowest precedence. It means that if there are</div> <div> * and + operators in an expression then first the * will be evaluated and then its result</div> <div> will be added to other operand. If there are * and / operators in an expression (both</div> <div> have the same precedence) then the operator which occurs first from left will be</div> <div> evaluated first and then the next, except you force any operator to evaluate by putting</div> <div> parentheses around it.</div> <div> The following table explains the precedence of the arithmetic operators:</div> <div> OPERATORS OPERATIONS PRECEDENCE (ORDER OF</div> <div> EVALUATION)</div> <div> ( ) Parentheses Evaluated first</div> <div> *, /, or % Multiplication,</div> <div> Division, Modulus</div> <div> Evaluated second. If there are</div> <div> several, they are evaluated from</div> <div> left to right</div> <div> + or - Addition, Subtraction Evaluated last. If there are several,</div> <div> they are evaluated from left to</div> <div> right</div> <div> Lets look some examples.</div> <div> What is the result of 10 + 10 * 5 ?</div> <div> The answer is 60 not 100. As * has higher precedence than + so 10 * 5 is evaluated</div> <div> first and then the answer 50 is added to 10 and we get the result 60. The answer will</div> <div> be 100 if we force the addition operation to be done first by putting 10 + 10 in</div> <div> parentheses. Thus the same expression rewritten as (10 + 10) * 5 will give the result</div> <div> 100. Note that how the parentheses affect the evaluation of an expression.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 23</div> <div> Similarly the expression 5 * 3 + 6 / 3 gives the answer 17, and not 7. The evaluation</div> <div> of this expression can be clarified by writing it with the use of parentheses as (5 * 3) +</div> <div> (6 / 3) which gives 15 + 2 = 17. Thus you should be careful while writing arithmetic</div> <div> expressions.</div> <div> Tips</div> <div> Use spaces in the coding to make it easy to read and understand</div> <div> Reserved words can not be used as variable names</div> <div> There is always a main( ) in a C program that is the starting point of execution</div> <div> Write one statement per line</div> <div> Type parentheses ’( )’ and braces ‘{ }’ in pairs</div> <div> Use parentheses for clarification in arithmetic expressions</div> <div> Don’t forget semicolon at the end of each statement</div> <div> C Language is case sensitive so variable names x and X are two different variables</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 24</div> <div> Lecture No. 4</div> <div> Reading Material</div> <div> Deitel & Deitel – C++ How to Program chapter 1</div> <div> 1.22</div> <div> Summary</div> <div> o Sample Program</div> <div> o Examples of Expressions</div> <div> o Use of Operators</div> <div> o Tips</div> <div> Sample Program</div> <div> Problem statement:</div> <div> Calculate the average age of a class of ten students. Prompt the user to enter the age of</div> <div> each student.</div> <div> Solution:</div> <div> Lets first sort out the problem. In the problem we will take the ages of ten students</div> <div> from the user. To store these ages we will use ten variables, one variable for each</div> <div> student’s age. We will take the ages of students in whole numbers (in years only, like</div> <div> 10, 12, 15 etc), so we will use the variables of data type int. The variables declaration</div> <div> statement in our program will be as follow:</div> <div> int age1, age2, age3, age4, age5, age6, age7, age8, age9, age10;</div> <div> We have declared all the ten variables in a single line by using comma separator ( , ).</div> <div> This is a short method to declare a number of variables of the same data type.</div> <div> After this we will add all the ages to get the total age and store this total age in a</div> <div> variable. Then we will get the average age of the ten students by dividing this total</div> <div> age by 10. For the storage of total and average ages we need variables. For this</div> <div> purpose we use variable TotalAge for the total of ages and AverageAge for average of</div> <div> ages respectively.</div> <div> int TotalAge, AverageAge;</div> <div> We have declared AverageAge as int data type so it can store only whole numbers.</div> <div> The average age of the class can be in real numbers with decimal point (for example if</div> <div> total age is 173 then average age will be 17.3). But the division of integers will</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 25</div> <div> produce integer result only and the decimal portion is truncated. If we need the actual</div> <div> result then we should use real numbers (float or double) in our program.</div> <div> Now we have declared variables for storing different values. In the next step we</div> <div> prompt the user to enter the age of first student. We simply show a text line on the</div> <div> screen by using the statement:</div> <div> cout << “Please enter the age of first student : ” ;</div> <div> So on the screen the sentence “Please enter the age of first student:” will appear.</div> <div> Whenever we are requesting user to enter some information we need to be very clear</div> <div> i.e. write such sentences that are self explanatory and user understands them</div> <div> thoroughly and correctly. Now with the above sentence everyone can understand that</div> <div> age would be entered for the first student. As we are expecting only whole numbers</div> <div> i.e. age in years only i.e. 10, 12 etc, our program is not to expect ages as 13.5 or 12.3</div> <div> or 12 years and 3 months etc. We can refine our sentence such, that the user</div> <div> understands precisely that the age would be entered in whole number only.</div> <div> After this we allow the user to enter the age. To, get the age entered by the user into a</div> <div> variable, we use the statement:</div> <div> cin >> age1;</div> <div> Lets have a look on the statement cin >> age1; cin is the counter part of the cout.</div> <div> Here cin is the input stream that gets data from the user and assigns it to the variable</div> <div> on its right side. We know that the sign >> indicates the direction of the flow of data.</div> <div> In our statement it means that data comes from user and is assigned to the variable</div> <div> age1, where age1 is a variable used for storing the age entered for student1. Similarly</div> <div> we get the ages of all the ten students and store them into respective variables. That</div> <div> means the age of first student in age1, the age of second student in age2 and so on up</div> <div> to 10 students. When cin statement is reached in a program, the program stops</div> <div> execution and expects some input from the user. So when cin >> age1; is executed,</div> <div> the program expects from the user to type the age of the student1. After entering the</div> <div> age, the user has to press the 'enter key'. Pressing 'enter key' conveys to the program</div> <div> that user has finished entering the input and cin assigns the input value to the variable</div> <div> on the right hand side which is age1 in this case. As we have seen earlier that in an</div> <div> assignment statement, we can have only one variable on left hand side of the</div> <div> assignment operator and on right hand side we can have an expression that evaluates</div> <div> to a single value. If we have an expression on the left hand side of assignment</div> <div> operator we get an error i.e. x = 2 + 4; is a correct statement but x + y = 3+ 5; is an</div> <div> incorrect statement as we can not have an expression on the left hand side. Similarly</div> <div> we can not have an expression after the >> sign with cin. So we can have one and</div> <div> only one variable after >> sign i.e. cin >> x; is a correct statement and cin >> x + y;</div> <div> is an incorrect statement.</div> <div> Next, we add all these values and store the result to the variable TotalAge. We use</div> <div> assignment operator for this purpose. On the right hand side of the assignment</div> <div> operator, we write the expression to add the ages and store the result in the variable,</div> <div> TotalAge on left hand side. For this purpose we write the statement as follow:</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 26</div> <div> TotalAge = age1 + age2 + age3 + age4 + age5 + age6 + age7 + age8 +</div> <div> age9 + age10 ;</div> <div> The expression on the right hand side uses many addition operators ( + ). As these</div> <div> operators have the same precedence, the expression is evaluated from left to right.</div> <div> Thus first age1 is added to age2 and then the result of this is added to age3 and then</div> <div> this result is added to age4 and so on.</div> <div> Now we divide this TotalAge by 10 and get the average age. We store this average</div> <div> age in the variable i.e. AverageAge by writing the statement:</div> <div> AverageAge = TotalAge / 10;</div> <div> And at the end we display this average age on the screen by using the following</div> <div> statement:</div> <div> cout << “ The average age of the students is : “ << AverageAge;</div> <div> Here the string enclosed in the quotation marks, will be printed on the screen as it is</div> <div> and the value of AverageAge will be printed on the screen.</div> <div> The complete coding of the program is given below:</div> <div> /* This program calculates the average age of a class of ten students after prompting</div> <div> the user to enter the age of each student. */</div> <div> #include <iostream.h></div> <div> main ()</div> <div> {</div> <div> // declaration of variables, the age will be in whole numbers</div> <div> int age1, age2, age3, age4, age5, age6, age7, age8, age9, age10;</div> <div> int TotalAge, AverageAge;</div> <div> // take ages of the students from the user</div> <div> cout << “Please enter the age of student 1: ”;</div> <div> cin >> age1;</div> <div> cout << “Please enter the age of student 2: ”;</div> <div> cin >> age2;</div> <div> cout << “Please enter the age of student 3: ”;</div> <div> cin >> age3;</div> <div> cout << “Please enter the age of student 4: ”;</div> <div> cin >> age4;</div> <div> cout << “Please enter the age of student 5: ”;</div> <div> cin >> age5;</div> <div> cout << “Please enter the age of student 6: ”;</div> <div> cin >> age6;</div> <div> cout << “Please enter the age of student 7: ”;</div> <div> cin >> age7;</div> <div> cout << “Please enter the age of student 8: ”;</div> <div> cin >> age8;</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 27</div> <div> cout << “Please enter the age of student 9: ”;</div> <div> cin >> age9;</div> <div> cout << “Please enter the age of student 10: ”;</div> <div> cin >> age10;</div> <div> // calculate the total age and average age</div> <div> TotalAge = age1 + age2 + age3 + age4 + age5 + age6 + age7 + age8 + age9 +</div> <div> age10;</div> <div> AverageAge = TotalAge / 10;</div> <div> // Display the result ( average age )</div> <div> cout << “Average age of class is: “ << AverageAge;</div> <div> }</div> <div> A sample output of the above program is given below.</div> <div> In the above output the total age of the students is 123 and the actual average should</div> <div> be 12.3 but as we are using integer data types so the decimal part is truncated and the</div> <div> whole number 12 is assigned to the variable AverageAge.</div> <div> Examples of Expressions</div> <div> We have already seen the precedence of arithmetic operators. We have expressions</div> <div> for different calculations in algebraic form, and in our programs we write them in the</div> <div> form of C statements. Let’s discuss some more examples to get a better</div> <div> understanding.</div> <div> We know about the quadratic equation in algebra, that is y = ax2 + bx + c. The</div> <div> quadratic equation in C will be written as y = a * x * x + b * x + c. In C, it is not an</div> <div> equation but an assignment statement. We can use parentheses in this statement, this</div> <div> Please enter the age of student 1: 12</div> <div> Please enter the age of student 2: 13</div> <div> Please enter the age of student 3: 11</div> <div> Please enter the age of student 4: 14</div> <div> Please enter the age of student 5: 13</div> <div> Please enter the age of student 6: 15</div> <div> Please enter the age of student 7: 12</div> <div> Please enter the age of student 8: 13</div> <div> Please enter the age of student 9: 14</div> <div> Please enter the age of student 10: 11</div> <div> Average age of class is: 12</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 28</div> <div> will make the expression statement easy to read and understand. Thus we can rewrite</div> <div> it as y = a * (x * x) + (b * y) + c.</div> <div> Note that we have no power operator in C, just use * to multiply the same value.</div> <div> Here is another expression in algebra: x = ax + by + cz2. In C the above expression</div> <div> will be as:</div> <div> x = a * x + b * y + c * z * z</div> <div> The * operator will be evaluated before the + operator. We can rewrite the above</div> <div> statement with the use of parentheses. The same expressions can be written as:</div> <div> x = (a * x) + (b * y) + c * ( z * z)</div> <div> Lets have an other expression in algebra as x = a(x + b(y + cz2)). The parentheses in</div> <div> this equation force the order of evaluation. This expression will be written in C as:</div> <div> x = a * (x + b * (y + c * z * z))</div> <div> While writing expressions in C we should keep in mind the precedence of the</div> <div> operators and the order of evaluation of the expressions (expressions are evaluated</div> <div> from left to right). Parentheses are used in complicated expressions. In algebra, there</div> <div> may be curly brackets { } and square brackets [ ] in an expression but in C we have</div> <div> only parentheses</div> <div> ( ). Using parentheses, we can make a complex expression easy to read and</div> <div> understand and can force the order of evaluation. We have to be very careful while</div> <div> using parentheses, as parentheses at wrong place can cause an incorrect result. For</div> <div> example, a statement x = 2 + 4 * 3 results x = 14. As * operator is of higher</div> <div> precedence, 4 * 3 is evaluated first and then result 12 is added to 4 which gives the</div> <div> result 14. We can rewrite this statement, with the use of parentheses to show it clearly,</div> <div> that multiplication is performed first. Thus we can write it as x = 2 + (4 * 3). But the</div> <div> same statement with different parentheses like x = (2 + 4) * 3 will give the result 18,</div> <div> so we have to be careful while using parenthesis and the evaluation order of the</div> <div> expression.</div> <div> Similarly the equation (b2 – 4ac)/2a can be written as ( b * b – 4 * a * c) / ( 2 * a ).</div> <div> The same statement without using parentheses will be as b * b – 4 * a * c / 2 * a. This</div> <div> is wrong as it evaluates to b2 – 4ac/2a (i.e. 4ac is divided by 2a instead of (b2-4ac)).</div> <div> Use of Operators</div> <div> Here are sample programs which will further explain the use of operators in</div> <div> programming.</div> <div> Problem Statement:</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 29</div> <div> Write a program that takes a four digits integer from user and shows the digits on the</div> <div> screen separately i.e. if user enters 7531, it displays 1,3,5,7 separately.</div> <div> Solution:</div> <div> Let’s first analyze the problem and find out the way how to program it.</div> <div> Analysis:</div> <div> First of all, we will sort the problem and find out how we can find digits of an integer.</div> <div> We know that when we divide a number by 10, we get the last digit of the number as</div> <div> remainder. For example when we divide 2415 by 10 we get 5 as remainder. Similarly</div> <div> 3476 divided by 10 gives the remainder 6. We will use this logic in our problem to get</div> <div> the digits of the number. First of all, we declare two variables for storing number and</div> <div> the digit. Let’s say that we have a number 1234 to show its digits separately. In our</div> <div> program we will use modulus operator ( % ) to get the remainder. So we get the first</div> <div> digit of the number 1234 by taking its modulus with 10 (i.e. 1234 % 10). This will</div> <div> give us the digit 4. We will show this digit on the screen by using cout statement.</div> <div> After this we have to find the next digit. For this we will divide the number by 10 to</div> <div> remove its last digit. Here for example the answer of 1234 divided by 10 is 123.4, we</div> <div> need only three digits and not the decimal part. In C we know that the integer division</div> <div> truncates the decimal part to give the result in whole number only. We will use integer</div> <div> division in our program and declare our variable for storing the number as int data</div> <div> type. We will divide the number 1234 by 10 (i.e. 1234 / 10). Thus we will get the</div> <div> number with remaining three digits i.e. 123. Here is a point to be noted that how can</div> <div> we deal with this new number (123)?</div> <div> There are two ways, one is that we declare a new variable of type int and assign the</div> <div> value of this new number to it. In this way we have to declare more variables that</div> <div> mean more memory will be used. The second way is to reuse the same variable</div> <div> (where number was already stored). As we have seen earlier that we can reassign</div> <div> values to variables like in the statement x = x + 1, which means, add 1 to the value of</div> <div> x and assign this resultant value again to x. In this way we are reusing the variable x.</div> <div> We will do the same but use the division operator instead of addition operator</div> <div> according to our need. For this purpose we will write number = number / 10. After</div> <div> this statement we have value 123 in the variable number.</div> <div> Again we will get the remainder of this number with the use of modulus operator,</div> <div> dividing the number by 10 (i.e. 123 % 10). Now we will get 3 and display it on the</div> <div> screen. To get the new number with two digits, divide the number by 10. Once again,</div> <div> we get the next digit of the number (i.e. 12) by using the modulus operator with 10,</div> <div> get the digit 2 and display it on the screen. Again get the new number by dividing it</div> <div> by 10</div> <div> (i.e. 1). We can show it directly, as it is the last digit, or take remainder by using</div> <div> modulus operator with 10. In this way, we get all the digits of the number.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 30</div> <div> Now let’s write the program in C by following the analysis we have made. The</div> <div> complete C program for the above problem is given below. It is easy to understand as</div> <div> we are already familiar with the statements used in it.</div> <div> /* A program that takes a four digits integer from user and shows the digits on the</div> <div> screen separately i.e. if user enters 7531, it displays 7,5,3,1 separately. */</div> <div> #include <iostream.h></div> <div> main()</div> <div> {</div> <div> // declare variables</div> <div> int number, digit;</div> <div> // prompt the user for input</div> <div> cout << "Please enter 4-digit number:";</div> <div> cin >> number;</div> <div> // get the first digit and display it on screen</div> <div> digit = number % 10;</div> <div> cout << "The digits are: ";</div> <div> cout << digit << ", ";</div> <div> // get the remaining three digits number</div> <div> number = number / 10;</div> <div> // get the next digit and display it</div> <div> digit = number % 10;</div> <div> cout << digit << ", ";</div> <div> // get the remaining two digits number</div> <div> number = number / 10;</div> <div> // get the next digit and display it</div> <div> digit = number % 10;</div> <div> cout << digit << ", ";</div> <div> // get the remaining one digit number</div> <div> number = number / 10;</div> <div> // get the next digit and display it</div> <div> digit = number % 10;</div> <div> cout << digit;</div> <div> }</div> <div> A sample output of the above program is given below.</div> <div> Please enter 4-digit number: 5678</div> <div> The digits are: 8, 7, 6, 5</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 31</div> <div> Problem Statement:</div> <div> Write a program that takes radius of a circle from the user and calculates the diameter,</div> <div> circumference and area of the circle and display the result.</div> <div> Solution:</div> <div> In this problem we take the input (radius of a circle) from the user. For that we can</div> <div> use cin statement to prompt the user to enter the radius of a circle. We store this radius</div> <div> in a variable. We also need other variables to store diameter, circumference and area</div> <div> of the circle. To obtain the correct result, we declare these variables of type float,</div> <div> instead of int data type, as we know that the int data type stores the whole numbers</div> <div> only. Here in our problem the area or circumference of the circle can be in decimal</div> <div> values. After getting the radius we use the formulae to find the diameter,</div> <div> circumference and area of the circle and then display these results on the screen. The</div> <div> solution of this program in coding form is given below.</div> <div> /* Following program takes the radius of a circle from the user and calculates the</div> <div> diameter, circumference and area of the circle and displays the result. */</div> <div> #include <iostream.h></div> <div> main ()</div> <div> {</div> <div> // declare variables</div> <div> float radius, diameter, circumference, area;</div> <div> // prompt the user for radius of a circle</div> <div> cout << "Please enter the radius of the circle " ;</div> <div> cin >> radius ;</div> <div> // calculate the diameter, circumference and area of the circle</div> <div> // implementing formula i.e. diameter = 2 r circumference = 2 ח r and area = ח r2</div> <div> diameter = radius * 2 ;</div> <div> circumference = 2 * 3.14 * radius ; // 3.14 is the value of ח (Pi)</div> <div> area = 3.14 * radius * radius ;</div> <div> // display the results</div> <div> cout << "The diameter of the circle is : " << diameter ;</div> <div> cout << "The circumference of the circle is : " << circumference ;</div> <div> cout << "The area of the circle is : " << area ;</div> <div> }</div> <div> A sample output of the above program is given below.</div> <div> Please enter the radius of the circle 5</div> <div> The diameter of the circle is : 10</div> <div> The circumference of the circle is : 31.4</div> <div> The area of the circle is : 78.5</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 32</div> <div> Tips</div> <div> o Use descriptive names for variables</div> <div> o Indent the code for better readability and understanding</div> <div> o Use parenthesis for clarity and to force the order of evaluation in an</div> <div> expression</div> <div> o Reuse the variables for better usage of memory</div> <div> o Take care of division by zero</div> <div> o Analyze the problem properly, and then start coding (i.e. first think and then</div> <div> write)</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 33</div> <div> Lecture No. 5</div> <div> Reading Material</div> <div> Deitel & Deitel – C++ How to Program chapter 2</div> <div> 2.4, 2.5, 2.6, 2.19,</div> <div> 2.20</div> <div> Summary</div> <div> o Conditional Statements</div> <div> o Flow Charting</div> <div> • Sample Program 1</div> <div> o if/else structure</div> <div> o Logical Operators</div> <div> • Sample Program 2</div> <div> o Tips</div> <div> Conditional Statements (Decision Making)</div> <div> In every day life, we are often making decisions. We perform different tasks while</div> <div> taking decisions. For example, the statement ‘if the milk shop is open, bring one liter</div> <div> of milk while returning home from college’, involves this phenomenon.</div> <div> In this statement, there is an element of decision making. We bring one litre of milk if</div> <div> the shop is open. And if the shop is closed, we come back to home without milk.</div> <div> Thus we are making a decision on the condition that the shop is open. The decisionmaking</div> <div> process is everywhere in our daily life. We see that the college gives</div> <div> admission to a student if he has the required percentage in his previous examination</div> <div> and/or in the entry test. Similarly administration of a basketball team of the college</div> <div> decides that the students having height more than six feet can be members of the</div> <div> team.</div> <div> In the previous lectures, we have written simple elementary programs. For writing</div> <div> interesting and useful programs, we have to introduce the decision making power in</div> <div> them. Now we will see what kind of decisions are there in programming and how</div> <div> these can be used.</div> <div> Every programming language provides a structure for decision making.</div> <div> 'C' also provides this structure. The statement used for decisions in 'C' language is</div> <div> known as the 'if statement'. The if statement has a simple structure. That is</div> <div> if ( condition )</div> <div> Statement (or group of statements)</div> <div> The above statements mean, If condition is true, then execute the statement or a group</div> <div> of statements. Here the condition is a statement which explains the condition on</div> <div> which a decision will be made. We can understand it from the example that Ali can</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 34</div> <div> become the member of the basket ball team if he has a height more than six feet .In</div> <div> this case, the condition will be</div> <div> if (Ali’s height is greater than six feet)</div> <div> Ali can be a member of team</div> <div> We have written the condition in English language. Now let's see how we can</div> <div> implement this in terms of variables, operators and C statements. In the program, we</div> <div> will write the condition in parentheses, followed by a statement or group of statements</div> <div> to be executed.</div> <div> Now here is the concept of block of statements. We use braces { } to make a group</div> <div> (block) of a number of statements. We put ‘{’ before first statement and ‘}’ after the</div> <div> last statement. Thus if we have to do many things after the if statement. The structure</div> <div> of if statement becomes as under</div> <div> if (condition)</div> <div> {</div> <div> statement;</div> <div> statement;</div> <div> .</div> <div> .</div> <div> statement;</div> <div> }</div> <div> Note the indentation of the lines and semi-colon after each statement. Semi-colons are</div> <div> necessary after every C statement. The indentation is only a matter of style. It makes</div> <div> the code easy to read and understand from where a block starts, ends and what kind of</div> <div> block it is. It does not affect the logic of the program. But the braces can affect the</div> <div> logic. We can also write a comment line to state the purpose of code block.</div> <div> Let's consider a simple example to explain the if statement. Suppose, we have ages of</div> <div> two students (say for the time being we have got these ages in variables). These</div> <div> variables are- age1 and age2. Now we say that if the age1 is greater than age2, then</div> <div> display the statement ‘Student 1 is older than student 2’.</div> <div> The coding for this program will be as below</div> <div> #include <iostream.h></div> <div> main()</div> <div> {</div> <div> int age1, age2;</div> <div> age1 = 12;</div> <div> age2 = 10;</div> <div> if(age1 > age2)</div> <div> cout << “Student 1 is older than student 2”;</div> <div> }</div> <div> Here, in our code we see a new operator i.e. ‘ > ‘ (greater than) in the if statement. We</div> <div> need such operators (like greater than, less than, equal to etc) while making decisions.</div> <div> These operators are called 'relational operators'. These are almost the same relational</div> <div> operators we use in algebra. Following table summarizes the relational operators.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 35</div> <div> Algebraic In C</div> <div> language</div> <div> Example Meaning</div> <div> Greater than > > x > y x is greater than y</div> <div> Equal to = == x == y x is equal to y</div> <div> Less than < < x < y x is less than y</div> <div> Greater than or</div> <div> equal to</div> <div> > >= x >= y x is greater than or</div> <div> equal to y</div> <div> Less than or</div> <div> equal to</div> <div> < <= x <= y x is less than or equal</div> <div> to y</div> <div> Not equal to ≠ != x != y x is not equal to y</div> <div> Note that there is no space between ==, >=, <= and !=.</div> <div> These are considered as single operators.</div> <div> The operator == (equal to) is different from the operator =. We know that operator =</div> <div> is the assignment operator which is used in assignment statement to assign a value to</div> <div> a variable.</div> <div> Don't confuse the assignment operator (=) with equal to operator (==). If we write</div> <div> single = in condition of if statement. For example, if we write if ( x = 2 ), the compiler</div> <div> will not give error. This means that it is not a syntax error. The conditional expression</div> <div> in if statement returns a value. In this case, x = 2 will also have some value but it will</div> <div> not in the form of true or false. So it will create a logical error. So be careful while</div> <div> using equal to condition in if statement.</div> <div> Flow Charting</div> <div> There are different techniques that are used to analyze and design a program. We will</div> <div> use the flow chart technique. A flow chart is a pictorial representation of a program.</div> <div> There are labeled geometrical symbols, together with the arrows connecting one</div> <div> symbol with other.</div> <div> A flow chart helps in correctly designing the program by visually showing the</div> <div> sequence of instructions to be executed. A programmer can trace and rectify the</div> <div> logical errors by first drawing a flow chart and then simulating it.</div> <div> Flow Chart Symbols</div> <div> Below are some of the main symbols used in the flow chart.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 36</div> <div> The flow chart for the if structure is shown in the figure below.</div> <div> Sample Program 1</div> <div> Now let’s see the usage of relational operators by an example. There are two students</div> <div> Amer and Amara. We take their ages from the user, compare them and tell who is</div> <div> older?</div> <div> As there are two students to be compared in terms of age, we need to declare two</div> <div> variables to store their ages. We declare two variables AmerAge and AmaraAge of</div> <div> type int. The variable names are one continuous word as we can’t use spaces in a</div> <div> variable name.</div> <div> Here is an important point about variables declaration. We should assign an initial</div> <div> value (preferably 0 for integers) to variables when we declare them. This is called</div> <div> initialization of variables.</div> <div> We can do this in one line while declaring a variable like int x = 0; This statement</div> <div> will declare a variable of name x with data type int and will assign a value 0 to this</div> <div> variable. Initializing a variable in this way is just a matter of style. You can initialize a</div> <div> variable on a separate line after declaring it. It is a good programming practice to</div> <div> initialize a variable.</div> <div> Now we prompt the user to enter Amer’s age and store it into variable AmerAge.</div> <div> Then similarly we get Amara’s age from the user in the variable AmaraAge.</div> <div> While comparing the ages, we will use the if statement to see whether Amer’s age is</div> <div> greater than Amara’s. We will use > (greater than) operator to compare the ages. This</div> <div> can be written as if ( AmerAge > AmaraAge) .</div> <div> With this if statement, we write the statement cout << "Amer is greater than Amara" ;</div> <div> It’s a simple one line test i.e. ‘if Amer’s age is greater than Amara's’, then display the</div> <div> message ‘Amer is older than Amara’.</div> <div> The flow chart for the above problem is as under.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 37</div> <div> The complete code of the program is given below.</div> <div> /* This program test that if the age of Amer is greater than Amara’s age and displays the result.</div> <div> */</div> <div> # include <iostream.h></div> <div> main ( )</div> <div> {</div> <div> int AmerAge, AmaraAge;</div> <div> //prompt the user to enter Amer’s age</div> <div> cout << “Please enter Amer’s age “ ;</div> <div> cin >> AmerAge;</div> <div> //prompt the user to enter Amara’s age</div> <div> cout << “Please enter Amara’s age “ ;</div> <div> cin >> AmaraAge;</div> <div> //perform the test</div> <div> if(AmerAge > AmaraAge )</div> <div> cout << “ Amer is older than Amara”;</div> <div> }</div> <div> In our program, we write a single statement with the if condition. This statement</div> <div> executes if the condition is true. If we want to execute more than one statements, then</div> <div> we have to enclose all these statements in curly brackets { }. This comprises a block</div> <div> of statements which will execute depending upon the condition. This block may</div> <div> contain a single statement just like in our problem. So we can write the if statement as</div> <div> follow.</div> <div> if (AmerAge > AmaraAge )</div> <div> {</div> <div> cout << " Amer is older than Amara";</div> <div> }</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 38</div> <div> A sample execution of the program provides the following output.</div> <div> Please enter Amer’s age 16</div> <div> Please enter Amara’s age 14</div> <div> Amer is older than Amara</div> <div> Now think what happens if the condition in the if statement is not true i.e. Amer’s age</div> <div> is not greater than Amara’s. In this case, if the user enters Amer’s age less than</div> <div> Amara’s, then our program does nothing. So to check this condition, another if</div> <div> statement after the first if statement is required. Then our program will be as:</div> <div> /* This program checks the age of Amer and Amara’s and</div> <div> displays the appropriate the message. The program is using</div> <div> two if statements.*/</div> <div> # include <iostream.h></div> <div> main ( )</div> <div> {</div> <div> int AmerAge, AmaraAge;</div> <div> //prompt the user to enter Amer’s age</div> <div> cout << “Please enter Amer’s age “ ;</div> <div> cin >> AmerAge;</div> <div> //prompt the user to enter Amara’s age</div> <div> cout << “Please enter Amara’s age “ ;</div> <div> cin >> AmaraAge;</div> <div> //perform the test</div> <div> if (AmerAge > AmaraAge )</div> <div> {</div> <div> cout << “ Amer is older than Amara”;</div> <div> }</div> <div> if (AmerAge < AmaraAge )</div> <div> {</div> <div> cout << “ Amer is younger than Amara”;</div> <div> }</div> <div> }</div> <div> Now our program decides properly about the ages entered by the user.</div> <div> After getting ages from the user, the if statements are tested and if statement will be</div> <div> executed if the condition evaluates to true.</div> <div> If/else Structure</div> <div> We have seen that the if structure executes its block of statement(s) only when the</div> <div> condition is true, otherwise the statements are skipped. The if/else structure allows the</div> <div> programmer to specify that a different block of statement(s) is to be executed when</div> <div> the condition is false. The structure of if/else selection is as follows.</div> <div> if ( condition)</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 39</div> <div> {</div> <div> statement(s);</div> <div> }</div> <div> else</div> <div> {</div> <div> statement(s);</div> <div> }</div> <div> Thus using this structure we can write the construct of our program as</div> <div> if (AmerAge > AmaraAge )</div> <div> {</div> <div> cout << " Amer is older than Amara";</div> <div> }</div> <div> else</div> <div> {</div> <div> cout << " Amer is younger than Amara";</div> <div> }</div> <div> In this construct, the program checks the condition in if statement .If the condition is</div> <div> true, then the line "Amer is greater than Amara" is printed. Otherwise (if condition is</div> <div> not true), the statement related to else is executed and the message "Amer is younger</div> <div> than Amara" is printed. Here in if/else structure an important thing is that the else part</div> <div> is executed for all the cases (conditions) other than the case which is stated in the if</div> <div> condition.</div> <div> And in the comparison, we know that there are three conditions i.e. first value is</div> <div> greater than the second value, first value is less than the second value and first value</div> <div> is equal to the second value. Here in the above program construct the else part</div> <div> competes the greater than conditions and covers both less than and equal to</div> <div> conditions.</div> <div> Thus in the above program construct, the message "Amer is younger than Amara" is</div> <div> displayed even if Amer’s age is the same as Amara’s age. This is logically incorrect</div> <div> and so to make this correct, we should display the message "Amer is younger than or</div> <div> is of the same age as Amara". Now this statement describes both the cases other than</div> <div> the one ‘Amer is greater than Amara'.</div> <div> The use of else saves us from writing different if statements to compare different</div> <div> conditions, in this way it cover the range of checks to complete the comparison.</div> <div> If we want to state the condition "Amer is greater than or is of the same age as</div> <div> Amara’s" then we use the greater than or equal to operator (i.e. >=) in the if statement</div> <div> and less than operator ( < ) in the else statement to complete the comparison.</div> <div> It is very important to check all the conditions while making decisions for good,</div> <div> complete and logical results. Make sure that all cases are covered and there is no such</div> <div> case in which the program does not respond.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 40</div> <div> Logical Operators</div> <div> There are many occasions when we face complex conditions to make a decision. This</div> <div> means that a decision depends upon more than one condition in different ways. Here</div> <div> we combine the conditions with AND or OR. For example, a boy can be selected in</div> <div> basket ball team only if he is more than 18 years old and has a height of 6 feet. In this</div> <div> statement a boy who wants to be selected in the basket ball team must have both the</div> <div> conditions fulfilled. This means that AND forces both the conditions to be true.</div> <div> Similarly we say that a person can be admitted to the university if he has a BCS</div> <div> degree OR BSC degree. In this statement, it is clear that a person will be admitted to</div> <div> the university if he has any one of the two degrees.</div> <div> In programming we use logical operators ( && and || ) for AND and OR respectively</div> <div> with relational operators. These are binary operators and take two operands. These</div> <div> operators use logical expressions as operands, which return TRUE or FALSE.</div> <div> The following table (called truth table) can be used to get the result of the &&</div> <div> operator and || operator with possible values of their operands. It is used to explain the</div> <div> result obtained by the && and || operators.</div> <div> Expression 1 Expression 2 Expression 1 &&</div> <div> Expression 2</div> <div> Expression 1 ||</div> <div> Expression 2</div> <div> True False false True</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 41</div> <div> True True true True</div> <div> False False false False</div> <div> False True false True</div> <div> The && operator has a higher precedence than the || operator. Both operators</div> <div> associate from left to right. An expressions containing && or || is evaluated only until</div> <div> truth or falsehood is known. Thus evaluation of the expression (age > 18) && (height</div> <div> > 6) will stop immediately if age > 18 is false (i.e. the entire expression is false) and</div> <div> continue if age > 18 is true (i.e. the entire expression could still be true if the</div> <div> condition height > 6 is true ).</div> <div> There is another logical operator that is called logical negation. The sign ! is used for</div> <div> this operator. This operand enables a programmer to ‘reverse’ the meaning of a</div> <div> condition. This is a unary operator that has only a single condition as an operand. The</div> <div> operator ! is placed before a condition. If the original condition (without the !</div> <div> operator) is false then the ! operator before it converts it to true and the statements</div> <div> attached to this are executed.</div> <div> Look at the following expression</div> <div> if ( ! (age > 18 ))</div> <div> cout << “ The age is less than 18”;</div> <div> Here the cout statement will be executed if the original condition (age > 18) is false</div> <div> because the ! operator before it reverses this false to true.</div> <div> The truth table for the logical negation operator ( ! ) is given below.</div> <div> Expression ! Expression</div> <div> True False</div> <div> False True</div> <div> Sample Program 2</div> <div> Problem statement</div> <div> A shopkeeper announces a package for customers that he will give 10 % discount on</div> <div> all bills and if a bill amount is greater than 5000 then a discount of 15 %. Write a C</div> <div> program which takes amount of the bill from user and calculates the payable amount</div> <div> by applying the above discount criteria and display it on the screen.</div> <div> Solution</div> <div> In this problem we are going to make decision on the basis of the bill amount, so we</div> <div> will be using if statement. We declare three variables amount, discount and</div> <div> netPayable and initialize them. Next we prompt the user to enter the amount of the</div> <div> bill. After this we implement the if statement to test the amount entered by the user.</div> <div> As we see in the problem statement that if the amount is greater than 5000 then the</div> <div> discount rate is 15 % otherwise (i.e. the amount is less than or equal to 5000) the</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 42</div> <div> discount rate is 10 %. So we check the amount in if statement. If it is greater than</div> <div> 5000 then the condition is true then the if block is executed otherwise if amount is not</div> <div> greater than 5000 then the else block is executed.</div> <div> The analysis and the flow of the program is shown by the following flow chart.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 43</div> <div> The complete program code is given below:</div> <div> /* This program calculates the discount amount for a customer. As different discount</div> <div> percentage applies on different amount so program is using if statement for deciding</div> <div> which discount is applicable and display the result. */</div> <div> # include <iostream.h></div> <div> main ( )</div> <div> {</div> <div> double amount, discount, netPayable ;</div> <div> amount = 0 ;</div> <div> netPayable = 0 ;</div> <div> discount = 0 ;</div> <div> // prompt the user to enter the bill amount</div> <div> cout << "Please enter the amount of the bill " ;</div> <div> cin >> amount ;</div> <div> //test the conditions and calculate net payable</div> <div> if ( amount > 5000 )</div> <div> {</div> <div> //calculate amount at 15 % discount</div> <div> discount = amount * (15.0 / 100);</div> <div> netPayable = amount - discount;</div> <div> cout << "The discount at the rate 15 % is Rupees " << discount << endl;</div> <div> cout << "The payable amount is Rupees " << netPayable ;</div> <div> }</div> <div> else</div> <div> {</div> <div> // calculate amount at 10 % discount</div> <div> discount = amount * (10.0 / 100);</div> <div> netPayable = amount - discount;</div> <div> cout << "The discount at the rate 10 % is Rupees " << discount << endl ;</div> <div> cout << "The payable amount is Rupees " << netPayable ;</div> <div> }</div> <div> }</div> <div> In the program we declared the variables as double. We do this to get the correct</div> <div> results (results may be in decimal points) of the calculations. Look at the statement</div> <div> which calculates the discount. The statement is</div> <div> discount = amount * (15.0 / 100) ;</div> <div> Here in the above statement we write 15.0 instead of 15. If we write here 15 then the</div> <div> division 15 / 100 will be evaluated as integer division and the result of division (0.15)</div> <div> will be truncated and we get 0 and this will result the whole calculation to zero. So it</div> <div> is necessary to write at least one operand in decimal form to get the correct result by</div> <div> division and we should also declare the variables as float or double. We do the same</div> <div> in the line discount = amount * (10.0 / 100);</div> <div> A sample execution of the program is given below</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 44</div> <div> Please enter the amount of the bill 6500</div> <div> The discount at the rate 15 % is Rupees 975</div> <div> The payable amount is Rupees 5525</div> <div> Tips</div> <div> • Always put the braces in an if/else structure</div> <div> • Type the beginning and ending braces before typing inside them</div> <div> • Indent both body statements of an if and else structure</div> <div> • Be careful while combining the conditions with logical operators</div> <div> • Use if/else structure instead of a number of single selection if</div> <div> statements</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 45</div> <div> Lecture No. 6</div> <div> Reading Material</div> <div> Deitel & Deitel – C++ How to Program chapter 2</div> <div> 2.7, 2.8, 2.9, 2.20</div> <div> Summary</div> <div> Repetition Structure (Loop)</div> <div> Overflow Condition</div> <div> Sample Program 1</div> </div> <div> <div> Sample Program 2</div> <div> Infinite Loop</div> <div> Properties of While loop</div> <div> Flow Chart</div> <div> Sample Program 3</div> <div> Tips</div> <div> Repetition Structure (Loop)</div> <div> In our day to day life, most of the things are repeated. Days and nights repeat</div> <div> themselves 30 times a month. Four seasons replace each other every year. We can see</div> <div> similar phenomenon in the practical life. For example, in the payroll system, some</div> <div> procedures are same for all the employees. These are repeatedly applied while dealing</div> <div> with the employees. So repetition is very useful structure in the programming.</div> <div> Let’s discuss a problem to understand it thoroughly. We have to calculate the sum of</div> <div> first 10 whole numbers i.e. add the numbers from 1 to 10. Following statement may</div> <div> be one way to do it.</div> <div> cout << “Sum of first 10 numbers is = “ << 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 +</div> <div> 10;</div> <div> This method is perfectly fine as the syntax is right. The answer is also correct. This</div> <div> procedure can also be adopted while calculating the sum of numbers from 1 to 100.</div> <div> We can write the above statement adding all the digits from 1 to 100. But this method</div> <div> will not be suitable for computing the sum of numbers from 1 to 1000.The addition of</div> <div> a very big number of digits will result in a very ugly and boring statement. Let’s</div> <div> analyze it carefully. Our first integer is 1, is there any other way to find out what is the</div> <div> next integer? Yes, we can add 1 to the integer and get the next integer which is 2. To</div> <div> find the next integer (i.e. 3) we add 1 to the previous integer (i.e. 2) and get the next</div> <div> integer which is 3. So whenever we have to find out the next integer, we have to add 1</div> <div> to the previous integer.</div> <div> We have to calculate the sum of first 1000 integers by taking a variable sum of type</div> <div> int. It is a good programming practice to initialize the variable before using it. Here,</div> <div> we initialize the variable sum with zero.</div> <div> int sum = 0;</div> <div> Now we get the first integer i.e. 1. We add this to the sum (sum becomes 0 + 1 = 1).</div> <div> Now get the next integer which can be obtained by adding 1 to the previous integer</div> <div> i.e. 2 and add it to the sum (sum becomes 1 + 2 = 3). Get the next integer by adding 1</div> <div> to the previous integer and add it to the sum (sum becomes 3 + 3 = 6) and so on.</div> <div> This way, we get the next integer by adding 1 to the previous integer and the</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 46</div> <div> new integer to the sum. It is obvious that we are repeating this procedure again and</div> <div> again i.e. adding 1 to the previous integer and add this new integer to the sum. So we</div> <div> need some repetition structure in the programming language. There are many looping</div> <div> constructs in C Language. The repetition structure we are discussing in this lecture is</div> <div> 'while loop structure'. ‘while’ is also a key word of 'C' so it cannot be used as a</div> <div> variable name.</div> <div> While means, 'do it until the condition is true'. The use of while construct can be</div> <div> helpful in repeating a set of instructions under some condition. We can also use curly</div> <div> braces with while just like we used with if. If we omit to use the braces with while</div> <div> construct, then only one statement after while will be repeatedly executed. For good</div> <div> programming practices, always use braces with while irrespective of the number of</div> <div> statements in while block. The code will also be indented inside the while block as</div> <div> Indentation makes the code easy to understand.</div> <div> The syntax of while construct is as under:</div> <div> while ( Logical Expression ) {</div> <div> statement1;</div> <div> statement2;</div> <div> ………….</div> <div> }</div> <div> The logical expression contains a logical or relational operator. While this logical</div> <div> expression is true, the statements will be executed repeatedly. When this logical</div> <div> expression becomes false, the statements within the while block, will not be executed.</div> <div> Rather the next statement in the program after while block, will be executed.</div> <div> Let’s discuss again the same problem i.e. calculation of the sum of first 1000 integers</div> <div> starting from 1. For this purpose, we need a variable to store the sum of integers and</div> <div> declare a variable named sum. Always use the self explanatory variable names. The</div> <div> declaration of the variable sum in this case is:</div> <div> int sum = 0;</div> <div> The above statement has performed two tasks i.e. it declared the variable sum of type</div> <div> int and also initialized it with zero. As it is good programming practice to initialize all</div> <div> the variables when declared, the above statement can be written as:</div> <div> int sum;</div> <div> sum = 0;</div> <div> Here we need a variable to store numbers. So we declare a variable number of type</div> <div> int. This variable will be used to store integers.</div> <div> int number;</div> <div> As we have declared another variable of int data type, so the variables of same data</div> <div> type can be declared in one line.</div> <div> int sum, number;</div> <div> Going back to our problem, we need to sum up all the integers from 1 to 1000. Our</div> <div> first integer is 1. The variable number is to be used to store integers, so we will</div> <div> initialize it by 1 as our first integer is 1:</div> <div> number = 1;</div> <div> Now we have two variables- sum and number. That means we have two memory</div> <div> locations labeled as sum and number which will be used to store sum of integers and</div> <div> integers respectively. In the variable sum, we have to add all the integers from 1 to</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 47</div> <div> 1000. So we will add the value of variable number into variable sum, till the time the</div> <div> value of number becomes 1000. So when the value of number becomes 1000, we will</div> <div> stop adding integers into sum. It will become the condition of our while loop. We can</div> <div> say sum the integers until integer becomes 1000. In C language, this condition can be</div> <div> written as:</div> <div> while ( number <= 1000 ) {</div> <div> ………Action ………</div> <div> }</div> <div> The above condition means, 'perform the action until the number is 1000 or less than</div> <div> 1000'. What will be the Action? Add the number, the value of number is 1 initially,</div> <div> into sum. This is a very simple statement:</div> <div> sum = sum + number;</div> <div> Let’s analyze the above statement carefully. We did not write sum = number; as this</div> <div> statement will replace the contents of sum and the previous value of sum will be</div> <div> wasted as this is an assignment statement. What we did? We added the contents of</div> <div> sum and contents of number first (i.e. 0 + 1) and then stored the result of this (i.e. 1) to</div> <div> the sum.</div> <div> Now we need to generate next integer and add it to the sum. How can we get the next</div> <div> integer? Just by adding 1 to the integer, we will get the next integer. In ‘C’, we will</div> <div> write it as:</div> <div> number = number + 1;</div> <div> Similarly in the above statement, we get the original contents of number (i.e. 1). Add</div> <div> 1 to them and then store the result (i.e. 2) into the number. Now we need to add this</div> <div> new number into sum:</div> <div> sum = sum + number;</div> <div> We add the contents of sum (i.e. 1) to the contents of number (i.e. 1) and then store</div> <div> the result (i.e. 2) to the sum. Again we need to get the next integer which can be</div> <div> obtained by adding 1 to the number. In other words, our action consists of only two</div> <div> statements i.e. add the number to the sum and get the next integer. So our action</div> <div> statements will be:</div> <div> sum = sum + number;</div> <div> number = number + 1;</div> <div> Putting the action statements in while construct:</div> <div> while ( number <= 1000 ) {</div> <div> sum = sum + number;</div> <div> number = number + 1;</div> <div> }</div> <div> Let's analyze the above while loop. Initially the contents of number is 1. The</div> <div> condition in while loop (i.e. number <= 1000) will be evaluated as true, contents of</div> <div> sum and contents of number will be added and the result will be stored into sum. Now</div> <div> 1 will be added to the contents of number and number becomes 2. Again the condition</div> <div> in while loop will be evaluated as true and the contents of sum will be added to the</div> <div> contents of number .The result will be stored into sum. Next 1 will be added to the</div> <div> contents of number and number becomes 3 and so on. When number becomes 1000,</div> <div> the condition in while loop evaluates to be true, as we have used <= (less than or equal</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 48</div> <div> to) in the condition. The contents of sum will be added to the contents of number (i.e.</div> <div> 1000) and the result will be stored into the sum. Next 1 will be added to the contents</div> <div> of number and number becomes 1001. Now the condition in while loop is evaluated to</div> <div> false, as number is no more less than or equal to 1000 (i.e. number has become 1001).</div> <div> When the condition of while loop becomes false, loop is terminated. The control of</div> <div> the program will go to the next statement following the ending brace of the while</div> <div> construct. After the while construct, we can display the result using the cout</div> <div> statement.</div> <div> cout << “ The sum of first 1000 integers starting from 1 is “ << sum;</div> <div> The complete code of the program is as follows:</div> <div> /* This program calculate the sum of first 1000 integers */</div> <div> #include <iostream.h></div> <div> main()</div> <div> {</div> <div> //declaration of variables</div> <div> int sum, number;</div> <div> //Initialization of the variables</div> <div> sum = 0;</div> <div> number = 1;</div> <div> // using the while loop to find out the sum of first 1000 integers starting from 1</div> <div> while(number <= 1000)</div> <div> {</div> <div> // Adding the integer to the contents of sum</div> <div> sum = sum + number;</div> <div> // Generate the next integer by adding 1 to the integer</div> <div> number = number + 1;</div> <div> }</div> <div> cout << "The sum of first 1000 integers starting from 1 is " << sum;</div> <div> }</div> <div> The output of the program is:</div> <div> The sum of first 1000 integers starting from 1 is 500500</div> <div> While construct is a very elegant and powerful construct. We have seen that it is very</div> <div> easy to sum first 1000 integers just with three statements. Suppose we have to</div> <div> calculate the sum of first 20000 integers. How can we do that? We just have to change</div> <div> the condition in the while loop (i.e. number <= 20000).</div> <div> Overflow Condition:</div> <div> We can change this condition to 10000 or even more. Just try some more numbers.</div> <div> How far can you go with the limit? We know that integers are allocated a fixed space</div> <div> in memory (i.e. 32 bits in most PCs) and we can not store a number which requires</div> <div> more bits than integer, into a variable of data type, int. If the sum of integers becomes</div> <div> larger than this limit (i.e. sum of integers becomes larger than 32 bits can store), two</div> <div> things can happen here. The program will give an error during execution, compiler</div> <div> can not detect such errors. These errors are known as run time errors. The second</div> <div> thing is that 32 bits of the result will be stored and extra bits will be wasted, so our</div> <div> result will not be correct as we have wasted the information. This is called overflow.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 49</div> <div> When we try to store larger information in, than a data type can store, overflow</div> <div> condition occurs. When overflow condition occurs either a run-time error is generated</div> <div> or wrong value is stored.</div> <div> Sample Program 1:</div> <div> To calculate the sum of 2000 integers, we will change the program (i.e. the while</div> <div> condition) in the editor and compile it and run it again. If we need to calculate the sum</div> <div> of first 5000 integers, we will change the program again in the editor and compile and</div> <div> run it again. We are doing this work again in a loop. Change the program in the editor,</div> <div> compile, execute it, again change the program, compile and execute it and so on. Are</div> <div> we doing this in a loop? We can make our program more intelligent so that we don’t</div> <div> need to change the condition every time. We can modify the condition as:</div> <div> int upperLimit;</div> <div> while (number <= upperLimit)</div> <div> where upperLimit is a variable of data type int. When the value of upperLimit is 1000,</div> <div> the program will calculate the sum of first 1000 integers. When the value of</div> <div> upperLimit is 5000, the program will calculate the sum of first 5000 integers. Now we</div> <div> can make it re-usable and more effective by requesting the user to enter the value for</div> <div> upper limit:</div> <div> cout << “Please enter the upper limit for which you want the sum ”;</div> <div> cin >> upperLimit;</div> <div> We don’t have to change our program every time when the limit changes. For the sum</div> <div> of integers, this program has become generic. We can calculate the sum of any</div> <div> number of integers without changing the program. To make the display statement</div> <div> more understandable, we can change our cout statement as:</div> <div> cout << “ The sum of first “ << upperLimit << “ integers is “ << sum;</div> <div> Sample Program 2:</div> <div> Problem statement:</div> <div> Calculate the sum of even numbers for a given upper limit of integers.</div> <div> Solution:</div> <div> We analyze the problem and know that while statement will be used. We need to sum</div> <div> even numbers only. How can we decide that a number is even or not? We know that</div> <div> the number that is divisible by 2 is an even number. How can we do this in C</div> <div> language? We can say that if a number is divisible by 2, it means its remainder is</div> <div> zero, when divided by 2. To get a remainder we can use C’s modulus operator i.e. %.</div> <div> We can say that for a number if the expression (number % 2) results in zero, the</div> <div> number is even. Putting this in a conditional statement:</div> <div> If ( ( number % 2) == 0 )</div> <div> The above conditional statement becomes true, when the number is even and false</div> <div> when the number is odd (A number is either even or odd).</div> <div> The complete code of the program is as follows:</div> <div> /* This program calculates sum of even numbers for a given upper limit of</div> <div> integers */</div> <div> #include <iostream.h></div> <div> main()</div> <div> {</div> <div> //declaration of variables</div> <div> int sum, number, upperLimit;</div> <div> //Initialization of the variables</div> <div> sum = 0;</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 50</div> <div> number = 1;</div> <div> // Prompt the user to enter upper limit of integers</div> <div> cout << “Please enter the upper limit for which you want the sum ” ;</div> <div> cin >> upperLimit;</div> <div> // using the while loop to find out the sum of first 1000 integers starting from 1</div> <div> while(number <= upperLimit)</div> <div> {</div> <div> // Adding the even integer to the contents of sum</div> <div> if ( ( number % 2 ) == 0 )</div> <div> {</div> <div> sum = sum + number;</div> <div> }</div> <div> // Generate the next integer by adding 1 to the integer</div> <div> number = number + 1;</div> <div> }</div> <div> cout << "The sum of even numbers of first “ << upperLimit << “ integers starting</div> <div> from 1 is " << sum;</div> <div> }</div> <div> The output of the program is:</div> <div> Please enter the upper limit for which you want the sum 10</div> <div> The sum of even numbers of first 10 integers starting from 1 is 30</div> <div> Suppose if we don’t have modulus operator in the C language. Is there any other way</div> <div> to find out the even numbers? We know that in C integer division gives the integer</div> <div> result and the decimal portion is truncated. So the expression (2 * (number / 2)) gives</div> <div> the number as a result, if the number is even only. So we can change our condition in</div> <div> if statement as:</div> <div> if ( ( 2 * ( number /2 ) ) == number )</div> <div> Infinite Loop:</div> <div> Consider the condition in the while structure that is (number <= upperLimit) and in</div> <div> the while block the value of number is changing (number = number + 1) to ensure that</div> <div> the condition is tested again next time. If it is true, the while block is executed and so</div> <div> on. So in the while block statements, the variable used in condition must change its</div> <div> value so that we have some definite number of repetitions. What will happen if we do</div> <div> not write the statement number = number + 1; in our program? The value of number</div> <div> will not change, so the condition in the while loop will be true always and the loop</div> <div> will be executed forever. Such loops in which the condition is always true are known</div> <div> as infinite loops as there are infinite repetitions in it.</div> <div> Property of while loop:</div> <div> In the above example, if the user enters 0, as the value for upper limit. In the while</div> <div> condition we test (number <= upperLimit) i.e. number is less than or equal to</div> <div> upperLimit ( 0 ), this test return false. The control of the program will go to the next</div> <div> statement after the while block. The statements in while structure will not be executed</div> <div> even for a single time. So the property of while loop is that it may execute zero or</div> <div> more time.</div> <div> The while loop is terminated, when the condition is tested as false. Make sure that the</div> <div> loop test has an adequate exit. Always use braces for the loop structure. If you forget</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 51</div> <div> to put the braces, only one statement after the while statement is considered in the</div> <div> while block.</div> <div> Flow Chart:</div> <div> The basic structure of while loop in structured flow chart is:</div> <div> At first, we will draw a rectangle and write while in it. Then draw a line to its right</div> <div> and use the decision symbol i.e. diamond diagram. Write the loop condition in the</div> <div> diamond and draw a line down to diamond which represents the flow when the</div> <div> decision is true. All the repeated processes are drawn here using rectangles. Then a</div> <div> line is drawn from the last process going back to the while and decision connection</div> <div> line. We have a line on the right side of diamond which is the exit of while loop. The</div> <div> while loop terminates, when the loop condition evaluates to false and the control gets</div> <div> out of while structure.</div> <div> Here is the flow chart for sample program 2:</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 52</div> <div> So far, we have been drawing flow charts after coding the program but actually we</div> <div> have to draw the flow chart first and then start coding.</div> <div> Sample Program 3:</div> <div> Problem statement:</div> <div> Calculate the factorial of a given number.</div> <div> Solution:</div> <div> The factorial of a number N is defined as:</div> <div> N(N-1)(N-2)………….3.2.1</div> <div> By looking at the problem, we can see that there is a repetition of multiplication of</div> <div> numbers. A loop is needed to write a program to solve a factorial of a number. Let's</div> <div> think in terms of writing a generic program to calculate the factorial so that we can get</div> <div> the factorial of any number. We have to multiply the number with the next</div> <div> decremented number until the number becomes 1. So the value of number will</div> <div> decrease by 1 in each repetition.</div> <div> Here is the flow chart for the factorial.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 53</div> <div> Here is the code of the program.</div> <div> /*This program calculates the factorial of a given number.*/</div> <div> #include <iostream.h></div> <div> main()</div> <div> {</div> <div> //declaration of variables</div> <div> int factorial, number;</div> <div> //Initialization of the variables</div> <div> factorial = 1;</div> <div> number = 1;</div> <div> // Prompt the user to enter upper limit of integers</div> <div> cout << “Please enter the number for factorial ” ;</div> <div> cin >> number;</div> <div> // using the while loop to find out the factorial</div> <div> while(number > 1)</div> <div> {</div> <div> factorial = factorial * number;</div> <div> number = number - 1;</div> <div> }</div> <div> cout << "The factorial is “ << factorial;</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 54</div> <div> }</div> <div> Exercise:</div> <div> Calculate the sum of odd integers for a given upper limit. Also draw flow chart of the</div> <div> program.</div> <div> Calculate the sum of even and odd integers separately for a given upper limit using</div> <div> only one loop structure. Also draw flow chart of the program.</div> <div> Tips</div> <div> Always use the self explanatory variable names</div> <div> Practice a lot. Practice makes a man perfect</div> <div> While loop may execute zero or more time</div> <div> Make sure that loop test (condition) has an acceptable exit.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 55</div> <div> Lecture No. 7</div> <div> Reading Material</div> <div> Deitel & Deitel – C++ How to Program Chapter 2</div> <div> 2.11, 2.12, 2.14, 2.15, 2.17</div> <div> Summary</div> <div> Do-While Statement</div> <div> Example</div> <div> for Statement</div> <div> Sample Program 1</div> <div> Increment/decrement Operators</div> <div> Sample Program 2</div> <div> Tips</div> <div> Do-While Statement</div> <div> We have seen that there may be certain situations when the body of while loop does</div> <div> not execute even a single time. This occurs when the condition in while is false. In</div> <div> while loop, the condition is tested first and the statements in the body are executed</div> <div> only when this condition is true. If the condition is false, then the control goes directly</div> <div> to the statement after the closed brace of the while loop. So we can say that in while</div> <div> structure, the loop can execute zero or more times. There may be situations where we</div> <div> may need that some task must be performed at least once.</div> <div> For example, a computer program has a character stored from a-z. It gives to</div> <div> user five chances or tries to guess the character. In this case, the task of guessing the</div> <div> character must be performed at least once. To ensure that a block of statements is</div> <div> executed at least once, C provides a do-while structure. The syntax of do-while</div> <div> structure is as under:</div> <div> do</div> <div> {</div> <div> statement(s);</div> <div> }</div> <div> while ( condition ) ;</div> <div> Here we see that the condition is tested after executing the statements of the loop</div> <div> body. Thus, the loop body is executed at least once and then the condition in do while</div> <div> statement is tested. If it is true, the execution of the loop body is repeated. In case, it</div> <div> proves otherwise (i.e. false), then the control goes to the statement next to the do</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 56</div> <div> while statement. This structure describes ‘execute the statements enclosed in braces in</div> <div> do clause' when the condition in while clause is true.</div> <div> Broadly speaking, in while loop, the condition is tested at the beginning of the loop</div> <div> before the body of the loop is performed. Whereas in do-while loop, the condition is</div> <div> tested after the loop body is performed.</div> <div> Therefore, in do-while loop, the body of the loop is executed at least once.</div> <div> The flow chart of do-while structure is as follow:</div> <div> Example</div> <div> Let’s consider the example of guessing a character. We have a character in the</div> <div> program to be guessed by the user. Let’s call it ‘z’. The program allows five tries</div> <div> (chances) to the user to guess the character. We declare a variable tryNum to store</div> <div> the number of tries. The program prompts the user to enter a character for guessing.</div> <div> We store this character in a variable c.</div> <div> We declare the variable c of type char. The data type char is used to store a single</div> <div> character. We assign a character to a variable of char type by putting the character in</div> <div> single quotes. Thus the assignment statement to assign a value to a char variable will</div> <div> be as c = ‘a’. Note that there should be a single character in single quotes. The</div> <div> statement like c = ‘gh’ will be a syntax error.</div> <div> Here we use the do-while construct. In the do clause we prompt the user to enter a</div> <div> character.</div> <div> After getting character in variable c from user, we compare it with our character i.e</div> <div> ‘z’. We use if\else structure for this comparison. If the character is the same as ours</div> <div> then we display a message to congratulate the user else we add 1 to tryNum variable.</div> <div> And then in while clause, we test the condition whether tryNum is less than or equal</div> <div> to 5 (tryNum <= 5). If this condition is true, then the body of the do clause is repeated</div> <div> again. We do this only when the condition (tryNum <= 5) remains true. If it is</div> <div> otherwise, the control goes to the first statement after the do-while loop.</div> <div> If guess is matched in first or second try, then we should exit the loop. We know that</div> <div> the loop is terminated when the condition tryNum <= 5 becomes false, so we assign a</div> <div> value which is greater than 5 to tryNum after displaying the message. Now the</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 57</div> <div> condition in the while statement is checked. It proves false (as tryNum is greater than</div> <div> 5). So the control goes out of the loop. First look here the flow chart for the program.</div> <div> The code of the program is given below.</div> <div> //This program allows the user to guess a character from a to z</div> <div> //do-while construct is used to allow five tries for guessing</div> <div> # include <iostream.h></div> <div> main ( )</div> <div> {</div> <div> //declare & initialize variables</div> <div> int tryNum = 0 ;</div> <div> char c ;</div> <div> // do-while construct</div> <div> do</div> <div> {</div> <div> cout << “Please enter a character between a-z for guessing : “ ;</div> <div> cin >> c ;</div> <div> //check the entered character for equality</div> <div> if ( c == ‘z’)</div> <div> {</div> <div> cout << “Congratulations, Your guess is correct” ;</div> <div> tryNum = 6;</div> <div> }</div> <div> else</div> <div> {</div> <div> tryNum = tryNum + 1;</div> <div> }</div> <div> }</div> <div> while ( tryNum <= 5);</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 58</div> <div> }</div> <div> There is an elegant way to exit the loop when the correct number is guessed. We</div> <div> change the condition in while statement to a compound condition. This condition will</div> <div> check whether the number of tries is less than or equal to 5 and the variable c is not</div> <div> equal to ‘z’. So we will write the while clause as while (tryNum <= 5 && c != ‘z’ );</div> <div> Thus when a single condition in this compound condition becomes false, then the</div> <div> control will exit the loop. Thus we need not to assign a value greater than 5 to variable</div> <div> tryNum. Thus the code of the program will be as:</div> <div> //This program allows the user to guess a character from a to z</div> <div> //do-while construct is used to allow five tries for guessing</div> <div> # include <iostream.h></div> <div> main ( )</div> <div> {</div> <div> //declare & initialize variables</div> <div> int tryNum = 0 ;</div> <div> char c ;</div> <div> // do-while construct, prompt the user to guess a number and compares it</div> <div> do</div> <div> {</div> <div> cout << “Please enter a character between a-z for guessing : “ ;</div> <div> cin >> c ;</div> <div> //check the entered character for equality</div> <div> if ( c == ‘z’)</div> <div> {</div> <div> cout << “Congratulations, Your guess is correct” ;</div> <div> }</div> <div> else</div> <div> {</div> <div> tryNum = tryNum + 1;</div> <div> }</div> <div> }</div> <div> while ( tryNum <= 5 && c != ‘z’ );</div> <div> }</div> <div> The output of the program is given below.</div> <div> Please enter a character between a-z for guessing : g</div> <div> Please enter a character between a-z for guessing : z</div> <div> Congratulations, Your guess is correct</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 59</div> <div> for Loop</div> <div> Let’s see what we do in a loop. In a loop, we initialize variable(s) at first. Then we set</div> <div> a condition for the continuation/termination of the loop. To meet the condition to</div> <div> terminate the loop, we affect the condition in the body of the loop. If there is a</div> <div> variable in the condition, the value of that variable is changed within the body of the</div> <div> loop. If the value of the variable is not changed, then the condition of termination of</div> <div> the loop will not meet and loop will become an infinite one. So there are three things</div> <div> in a loop structure i.e. (i) initialization, (ii) a continuation/termination condition and</div> <div> (iii) changing the value of the condition variable, usually the increment of the variable</div> <div> value.</div> <div> To implement these things, C provides a loop structure known as for loop. This is the</div> <div> most often used structure to perform repetition tasks for a known number of</div> <div> repetitions. The syntax of for loop is given below.</div> <div> for ( initialization condition ; continuation condition ; incrementing condition )</div> <div> {</div> <div> statement(s) ;</div> <div> }</div> <div> We see that a 'for statement' consists of three parts. In initialization condition, we</div> <div> initialize some variable while in continuation condition, we set a condition for the</div> <div> continuation of the loop. In third part, we increment the value of the variable for</div> <div> which the termination condition is set.</div> <div> Let's suppose, we have a variable counter of type int. We write for loop in our</div> <div> program as</div> <div> for ( counter = 0 ; counter < 10 ; counter = counter +1 )</div> <div> {</div> <div> cout << counter << endl;</div> <div> }</div> <div> This 'for loop' will print on the screen 0, 1, 2 …. 9 on separate lines (as we use endl in</div> <div> our cout statement). In for loop, at first, we initialize the variable counter to 0. And in</div> <div> the termination condition, we write counter < 10. This means that the loop will</div> <div> continue till value of counter is less than 10. In other words, the loop will terminate</div> <div> when the value of counter is equal to or greater than 10. In the third part of for</div> <div> statement, we write counter = counter + 1 this means that we add 1 to the existing</div> <div> value of counter. We call it incrementing the variable.</div> <div> Now let's see how this loop executes. When the control goes to for statement first</div> <div> time, it sets the value of variable counter to 0, tests the condition (i.e. counter < 10). If</div> <div> it is true, then executes the body of the loop. In this case, it displays the value of</div> <div> counter which is 0 for the first execution. Then it runs the incrementing statement (i.e.</div> <div> counter = counter + 1 ). Thus the value of counter becomes 1. Now, the control goes</div> <div> to for statement and tests the condition of continuation. If it is true, then the body of</div> <div> the loop is again executed which displays 1 on the screen. The increment statement is</div> <div> again executed and control goes to for statement. The same tasks are repeated. When</div> <div> the value of counter becomes 10, the condition counter < 10 becomes false. Then the</div> <div> loop is terminated and control goes out of for loop.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 60</div> <div> The point to be noted is that, the increment statement (third part of for statement) is</div> <div> executed after executing the body of the loop. Thus for structure is equivalent to a</div> <div> while structure, in which, we write explicit statement to change</div> <div> (increment/decrement) the value of the condition variable after the last statement of</div> <div> the body. The for loop does this itself according to the increment statement in the for</div> <div> structure. There may be a situation where the body of for loop, like while loop, may</div> <div> not be executed even a single time. This may happen if the initialization value of the</div> <div> variable makes the condition false. The statement in the following for loop will not be</div> <div> executed even a single time as during first checking, the condition becomes false. So</div> <div> the loop terminates without executing the body of the loop.</div> <div> for ( counter = 5 ; counter < 5 ; counter ++)</div> <div> {</div> <div> cout << “The value of counter is “ << counter ;</div> <div> }</div> <div> Sample Program 1</div> <div> Let’s take an example to explain for loop. We want to write a program that prints the</div> <div> table of 2 on the screen.</div> <div> In this program, we declare a variable counter of type int. We use this variable to</div> <div> multiply it by 2 with values 1 to 10. For writing the table of 2, we multiply 2 by 1, 2,</div> <div> 3 .. upto 10 respectively and each time display the result on screen. So we use for loop</div> <div> to perform the repeated multiplication.</div> <div> Following is the code of the program that prints the table of 2.</div> <div> //This program display the table of 2 up to multiplier 10</div> <div> # include <iostream.h></div> <div> main ( )</div> <div> {</div> <div> int counter;</div> <div> //the for loop</div> <div> for ( counter = 1 ; counter <= 10 ; counter = counter + 1)</div> <div> {</div> <div> cout << “2 x “ << counter << “ = “ << 2 * counter << “\n” ;</div> <div> }</div> <div> }</div> <div> This is a simple program. In the for statement, we initialize the variable counter to 1</div> <div> as we want the multiplication of 2 starting from 1. In the condition clause, we set the</div> <div> condition counter <= 10 as we want to repeat the loop for 10 times. And in the</div> <div> incrementing clause, we increment the variable counter by 1.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 61</div> <div> In the body of the for loop, we write a single statement with cout. This single</div> <div> statement involves different tasks. The portion ‘<< “2 x “’ displays the string “2 x “</div> <div> on the screen. After this, the next part ‘<< counter’ will print the value of counter.</div> <div> The ‘<< “ = ”’ will display ‘ = ‘ and then the next part ‘<< 2 * counter’ will display</div> <div> the result of 2 multiply by counter and the last <<”\n” ( the new line character) will</div> <div> start a new line. Thus in the first iteration where the value of counter is 1, the cout</div> <div> statement will display the following line</div> <div> 2 x 1 = 2</div> <div> After the execution of cout statement, the for statement will increment the counter</div> <div> variable by 1. Thus value of counter will be 2. Then condition will be checked which</div> <div> is still true. Thus the body of for loop (here the cout statement) will be executed again</div> <div> having the value of counter 2. So the following line will be printed.</div> <div> 2 x 2 = 4</div> <div> The same action will be repeated 10 times with values of counter from 1 to 10. When</div> <div> the value of counter is 11, the condition ( counter <= 10 ) will become false and the</div> <div> loop will terminate.</div> <div> The output of the above program is as the following.</div> <div> 2 x 1 = 2</div> <div> 2 x 2 = 4</div> <div> 2 x 3 = 6</div> <div> 2 x 4 = 8</div> <div> 2 x 5 = 10</div> <div> 2 x 6 = 12</div> <div> 2 x 7 = 14</div> <div> 2 x 8 = 16</div> <div> 2 x 9 = 18</div> <div> 2 x 10 = 20</div> <div> Now what will we do, if some one says us to write a table of 3, or 4 or 8 or any other</div> <div> number. Here comes the point of re-usability and that a program should be generic.</div> <div> We write a program in which a variable is used instead of a hard code number. We</div> <div> prompt the user to enter the number for which he wants a table. We store this number</div> <div> in the variable and then use it to write a table. So in our previous example, we now</div> <div> use a variable say number where we were using 2. We also can allow the user to</div> <div> enter the number of multipliers up to which he wants a table. For this, we use a</div> <div> variable maxMultiplier and execute the loop for maxMultiplier times by putting the</div> <div> condition counter <= maxMultiplier. Thus our program becomes generic which can</div> <div> display a table for any number and up to any multiplier.</div> <div> Thus, the code of our program will be as below:</div> <div> //This program takes an integer input from user and displays its table</div> <div> //The table is displayed up to the multiplier entered by the user</div> <div> # include <iostream.h></div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 62</div> <div> main ( )</div> <div> {</div> <div> int counter, number, maxMultiplier ;</div> <div> // Prompt the user for input</div> <div> cout << “Please enter the number for which you want a table : “ ;</div> <div> cin >> number ;</div> <div> cout << “Please enter the multiplier up to which you want a table : “ ;</div> <div> cin >> maxMultiplier ;</div> <div> //the for loop</div> <div> for ( counter = 1 ; counter <= maxMultiplier ; counter = counter + 1)</div> <div> {</div> <div> cout << number << “ x “ << counter << “ = “ << number * counter << “\n” ;</div> <div> }</div> <div> }</div> <div> The output of the program is shown as follows:</div> <div> Please enter the number for which you want a table : 7</div> <div> Please enter the multiplier up to which you want a table : 8</div> <div> 7 x 1 = 7</div> <div> 7 x 2 = 14</div> <div> 7 x 3 = 21</div> <div> 7 x 4 = 28</div> <div> 7 x 5 = 35</div> <div> 7 x 6 = 42</div> <div> 7 x 7 = 49</div> <div> 7 x 8 = 56</div> <div> Here is a guideline for programming style. We should avoid using constant values in</div> <div> our calculations or in long routines. The disadvantage of this is that if we want to</div> <div> change that constant value later, then we have to change every occurrence of that</div> <div> value in the program. Thus we have to do a lot of work and there may be some places</div> <div> in code where we do not change that value. To avoid such situations, we can use a</div> <div> variable at the start and assign that constant value to it and then in the program use</div> <div> that variable. Thus, if we need to change the constant value, we can assign the new</div> <div> value to that variable and the remaining code will remain the same. So in our program</div> <div> where we wrote the table of 2, we can use a variable (say number) and assign it the</div> <div> value 2. And in cout statement we use this variable instead of constant 2. If we want</div> <div> that the program should display a table of 5, then we just change the value of the</div> <div> variable. So for good programming, use variables for constant values instead of</div> <div> explicit constant values.</div> <div> Increment Decrement Operators</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 63</div> <div> We have seen that in while, do-while and for loop we write a statement to increase the</div> <div> value of a variable. For example, we used the statements like counter = counter + 1;</div> <div> which adds 1 to the variable counter. This increment statement is so common that it is</div> <div> used almost in every repetition structure (i.e. in while, do-while and for loop). The C</div> <div> language provides a unary operator that increases the value of its operator by 1. This</div> <div> operator is called increment operator and sign ++ is used for this. The statement</div> <div> counter = counter + 1; can be replaced with the statement</div> <div> counter ++ ;</div> <div> The statement counter++ adds 1 to the variable counter. Similarly the expressions i =</div> <div> i + 1 ; and j = j + 1 ; are equivalent to i++ ; and j++; respectively. There is also an</div> <div> operator -- called decrement operator. This operator decrements, the value of its</div> <div> operand by 1. So the statements counter = counter - 1; and j = j - 1; are equivalent to</div> <div> counter--; and j--; respectively.</div> <div> The increment operator is further categorized as pre-increment and post-increment.</div> <div> Similarly, the decrement operator, as pre-decrement and post-decrement.</div> <div> In pre-increment, we write the sign before the operand like ++j while in postincrement,</div> <div> the sign ++ is used after the operand like j++. If we are using only variable</div> <div> increment, pre or post increment does not matter. In this case, j++ is equivalent to</div> <div> ++j. The difference of pre and post increment matters when the variable is used in an</div> <div> expression where it is evaluated to assign a value to another variable. If we use preincrement</div> <div> ( ++j ), the value of j is first increased by 1. This new value is used in the</div> <div> expression. If we use post increment ( j++ ),the value of j is used in the expression.</div> <div> After that it is increased by 1. Same is the case in pre and post decrement.</div> <div> If j = 5, and we write the expression</div> <div> x = ++ j ;</div> <div> After the evaluation of this expression, the value of x will be 6 (as j is incremented</div> <div> first and then is assigned to x). The value of j will also be 6 as ++ operator increments</div> <div> it by 1.</div> <div> If j = 5, and we write the expression</div> <div> x = j++ ;</div> <div> Then after the evaluation of the expression, the value of x will be 5 (as the value of j</div> <div> is used before increment) and the value of j will be 6.</div> <div> The same phenomenon is true for the decrement operator with the difference that it</div> <div> decreases the value by 1. The increment and decrement operators affect the variable</div> <div> and update it to the new incremented or decremented value.</div> <div> The operators ++ and -- are used to increment or decrement the variable by 1. There</div> <div> may be cases when we are incrementing or decrementing the value of a variable by a</div> <div> number other than 1. For example, we write counter = counter + 5; or j = j – 4;. Such</div> <div> assignments are very common in loops, so C provides operators to perform this task</div> <div> in short. These operators do two things they perform an action (addition, subtraction</div> <div> etc) and do some assignment.</div> <div> These operators are +=, -=, *=, /= and %=. These operators are compound assignment</div> <div> operators. These operators assign a value to the left hand variable after performing an</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 64</div> <div> action (i.e. +, -, *, / and %). The use of these operators is explained by the following</div> <div> examples.</div> <div> Let’s say we have an expression, counter = counter + 5;. The equivalent of this</div> <div> expression is counter += 5;. The statement counter += 5; does two tasks. At first, it</div> <div> adds 5 to the value of counter and then assigns this result to counter. Similarly the</div> <div> following expressions</div> <div> x = x + 4 ;</div> <div> x = x - 3 ;</div> <div> x = x * 2 ;</div> <div> x = x / 2 ;</div> <div> x = x % 3;</div> <div> can be written in equivalent short statements using the operators ( +=, -=, *=, /=, %= )</div> <div> as follows</div> <div> x += 4 ;</div> <div> x -= 3 ;</div> <div> x *= 2;</div> <div> x /= 2;</div> <div> x %= 3 ;</div> <div> Note that there is no space between these operators. These are treated as single signs.</div> <div> Be careful about the operator %=. This operator assigns the remainder to the variable.</div> <div> These operators are alternate in short hand for an assignment statement. The use of</div> <div> these operators is not necessary. A programmer may use these or not. It is a matter of</div> <div> style.</div> <div> Example Program 2</div> <div> Let’s write a program using for loop to find the sum of the squares of the integers</div> <div> from 1 to n. Where n is a positive value entered by the user (i.e. Sum = 12 + 22 + 32 +</div> <div> ……+ n2)</div> <div> The code of the program is given below:</div> <div> //This program displays the sum of squares of integers from 1 to n</div> <div> # include <iostream.h></div> <div> main ( )</div> <div> {</div> <div> //declare and initialize variables</div> <div> int i, n, sum;</div> <div> sum = 0 ;</div> <div> //get input from user and construct a for loop</div> <div> cout << “Please enter a positive number for sum of squares: ” ;</div> <div> cin >> n;</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 65</div> <div> for ( i = 1 ; i <= n ; i ++)</div> <div> {</div> <div> sum += i * i ;</div> <div> }</div> <div> cout << “The sum of the first ” << n << “ squares is “ << sum << endl ;</div> <div> }</div> <div> In the program declared three variables i, n and sum. We prompted the user to enter a</div> <div> positive number. We stored this number in the variable n. Then we wrote a for loop.</div> <div> In the initialization part, we initialized variable i with value 1 to start the counting</div> <div> from 1. In the condition statement we set the condition i less than or equal to n</div> <div> (number entered by the user) as we want to execute the loop n times. In the increment</div> <div> statement, we incremented the counter variable by 1. In the body of the for loop we</div> <div> wrote a single statement sum += i * i ;. This statement takes the square of the counter</div> <div> variable ( i )and adds it to the variable sum. This statement is equivalent to the</div> <div> statement sum = sum + ( i * i ) ; Thus in each iteration the square of the counter</div> <div> variable (which is increased by 1 in each iteration ) is added to the sum. Thus loop</div> <div> runs n times and the squares of numbers from 1 to n are summed up. After</div> <div> completing the for loop the cout statement is executed which displays the sum of the</div> <div> squares of number from 1 to n.</div> <div> Following is the output when the number 5 is entered.</div> <div> Please enter a positive number for sum of squares: 5</div> <div> The sum of the first 5 squares is 55</div> <div> Tips</div> <div> Comments should be meaningful, explaining the task</div> <div> Don’t forget to affect the value of loop variable in while and do-while loops</div> <div> Make sure that the loop is not an infinite loop</div> <div> Don’t affect the value of loop variable in the body of for loop, the for loop does this</div> <div> by itself in the for statement</div> <div> Use pre and post increment/decrement operators cautiously in expressions</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 66</div> <div> Lecture No. 8</div> <div> Reading Material</div> <div> Deitel & Deitel – C++ How to Program Chapter 2</div> <div> 2.16, 2.18</div> <div> Summary</div> <div> o Switch Statement</div> <div> o Break Statement</div> <div> o Continue Statement</div> <div> o Guide Lines</div> <div> o Rules for structured Programming/Flow Charting</div> <div> o Sample Program</div> <div> o Tips</div> <div> Switch Statement</div> <div> Sometimes, we have multiple conditions and take some action according to each</div> <div> condition. For example, in the payroll of a company, there are many conditions to</div> <div> deduct tax from the salary of an employee. If the salary is less than Rs. 10000, there is</div> <div> no deduction. But if it falls in the slab Rs. 10000 - 20000, then the income tax is</div> <div> deducted. If it exceeds the limit of Rs. 20000, some additional tax will be deducted.</div> <div> So the appropriate deduction is made according to the category or slab of the salary.</div> <div> We can also understand this from the example of grades secured by the students of a</div> <div> class. Suppose we want to print description of the grade of a student. If the student has</div> <div> grade ‘A’ we print ‘Excellent’ and 'Very good', 'good', 'poor' and 'fail' for grades B,</div> <div> C, D, and F respectively. Now we have to see how this multi-condition situation can</div> <div> be applied in a program. We have a tool for decision making i.e. 'if statement'. We can</div> <div> use 'if statement' to decide what description for a grade should be displayed. So we</div> <div> check the grade in if statement and display the appropriate description. We have five</div> <div> categories of grades-- A, B, C, D, and F. We have to write five if statements to check</div> <div> all the five possibilities (probabilities) of grade. So we write this in our program as</div> <div> underif</div> <div> ( grade == ‘A’ )</div> <div> cout << “Excellent” ;</div> <div> if ( grade == ‘B’ )</div> <div> cout << “Very Good” ;</div> <div> if ( grade == ‘C’ )</div> <div> cout << “Good” ;</div> <div> if ( grade == ‘D’ )</div> <div> cout << “Poor” ;</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 67</div> <div> if ( grade == ‘F’ )</div> <div> cout << “Fail” ;</div> <div> These statements are correct and perform the required task. But the 'if statement' is</div> <div> computationally one of the most expensive statements in a program. We call it</div> <div> expensive due to the fact that the processor has to go through many cycles to execute</div> <div> an if statement to evaluate a single decision. So to make a program more efficient, try</div> <div> to use the minimum number of if statements. This will make the performance of the</div> <div> program better.</div> <div> So if we have different conditions in which only one will be true as seen in the</div> <div> example of student’s grades, the use of if statement is very expensive. To avoid this</div> <div> expensiveness, an alternate of multiple if statements can be used that is if/else</div> <div> statements. We can write an if statement in the body of an if statement which is</div> <div> known as nested if. We can write the previous code of if statements in the following</div> <div> nested if/else form.</div> <div> If ( grade == ‘A’ )</div> <div> cout << “Excellent” ;</div> <div> else if ( grade == ‘B’ )</div> <div> cout << “Very Good” ;</div> <div> else if ( grade == ‘C’ )</div> <div> cout << “Good” ;</div> <div> else if ( grade == ‘D’ )</div> <div> cout << “Poor” ;</div> <div> else if ( grade == ‘F’ )</div> <div> cout << “Fail” ;</div> <div> In the code, there is single statement with each if statement. If there are more</div> <div> statements with an if statement, then don’t forget the use of braces and make sure that</div> <div> they match (i.e. there is a corresponding closing brace for an opening brace). Proper</div> <div> indentation of the blocks should also be made.</div> <div> In the above example, we see that there are two approaches for a multi way decision.</div> <div> In the first approach, we use as many if statements as needed. This is an expensive</div> <div> approach. The second is the use of nested if statements. The second is little more</div> <div> efficient than the first one. In the 'nested if statements' the nested else is not executed</div> <div> if the first if condition is true and the control goes out of the if block.</div> <div> The C language provides us a stand-alone construct to handle these instances. This</div> <div> construct is switch structure. The switch structure is a multiple-selection construct</div> <div> that is used in such cases (multi way decisions) to make the code more efficient and</div> <div> easy to read and understand.</div> <div> The syntax of switch statement is as follows.</div> <div> switch ( variable/expression )</div> <div> {</div> <div> case constant1 : statementLlist1 ;</div> <div> case constant2 : statementLlist2 ;</div> <div> :</div> <div> :</div> <div> case constantN : statementListN ;</div> <div> default : statementList ;</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 68</div> <div> }</div> <div> In the switch statement, there should be an integer variable (also include char) or an</div> <div> expression which must evaluate an integer type (whole numbers only, the decimal</div> <div> numbers 2.5, 14.3 etc are not allowed). We can’t use compound conditions (i.e. the</div> <div> conditions that use logical operators && or ||) in switch statement and in case</div> <div> statements. The constants also must be integer constants (which include char). We</div> <div> can’t use a variable name with the case key word. The default statement is optional. If</div> <div> there is no case which matches the value of the switch statement, then the statements</div> <div> of default are executed.</div> <div> The switch statement takes the value of the variable, if there is an expression then it</div> <div> evaluates the expression and after that looks for its value among the case constants. If</div> <div> the value is found among the constants listed in cases, the statements in that</div> <div> statementList are executed. Otherwise, it does nothing. However if there is a default</div> <div> (which is optional), the statements of default are executed.</div> <div> Thus our previous grade example will be written in switch statement as below.</div> <div> switch ( grade )</div> <div> {</div> <div> case ‘A’ : cout << “Excellent” ;</div> <div> case ‘B’ : cout << “Very Good” ;</div> <div> case ‘C’ : cout << “Good” ;</div> <div> case ‘D’ : cout << “Poor” ;</div> <div> case ‘F’ : cout << “Fail” ;</div> <div> }</div> <div> We know that C language is 'case sensitive'. In this language, ‘A’ is different from</div> <div> ‘a’. Every character has a numeric value which is stored by the computer.. The</div> <div> numeric value of a character is known as ASCII code of the character. The ASCII</div> <div> code of small letters (a, b, c etc ) are different from ASCII code of capital letters (A,</div> <div> B, C etc). We can use characters in switch statement as the characters are represented</div> <div> as whole numbers inside the computers.</div> <div> Now we will see how the use of ' the letter a' instead of 'A' can affect our program.</div> <div> We want our program to be user- friendly. We don’t want to restrict the user to enter</div> <div> the grade in capital letters only. So we have to handle both small and capital letters in</div> <div> our program. Here comes the limitations of switch statement. We can’t say in our</div> <div> statement like</div> <div> case ‘A’ or ‘a’ : statements ;</div> <div> We have to make two separate cases so we write</div> <div> case ‘A” :</div> <div> case ‘a’ :</div> <div> statements;</div> <div> In the switch statement, the cases fall through the case which is true. All the</div> <div> statements after that case will be executed right down to the end of the switch</div> <div> statement. This is very important to understand it. Let's suppose that the user enters</div> <div> grade ‘B’. Now the case ‘A’ is skipped. Next case ‘B’ matches and statement cout <<</div> <div> “Very Good” ; is executed. After that, all the statements will be executed. So cout <<</div> <div> “Good” ; cout << “Poor” ;and cout << “Fail” ; will be executed after one another.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 69</div> <div> We don’t want this to happen. We want that when a case matches, then after</div> <div> executing its statement, the control should jump out of the switch statement leaving</div> <div> the other cases. For this purpose we use a key word break.</div> <div> Break Statement</div> <div> The break statement interrupts the flow of control. We have seen in switch statement</div> <div> that when a true case is found, the flow of control goes through every statement down</div> <div> ward. We want that only the statements of true case should be executed and the</div> <div> remaining should be skipped. For this purpose, we use the break statement. We write</div> <div> the break statement after the statements of a case. Thus, when a true case is found and</div> <div> its statements are executed then the break statement interrupts the flow of control and</div> <div> the control jumps out of the switch statement. If we want to do the same task for two</div> <div> cases, like in previous example for ‘A’ and ‘a’, then we don't put break statement</div> <div> after the first case. We write both the cases (or the cases may be more than two) line</div> <div> by line then write the common statements to be executed for these cases. We write the</div> <div> break statement after these common statements. We should use the break statement</div> <div> necessarily after the statements of each case. The break statement is necessary in</div> <div> switch structure, without it the switch structure becomes illogic. As without it all the</div> <div> statement will execute after first match case is found.</div> <div> The above code does nothing if the grade is other than these five categories (i.e. A, B,</div> <div> C, D and F). To handle all the possibilities of grade input, we write a default</div> <div> statement after the last case. The statement in this default case is executed if no case</div> <div> matches the grade. So in our program, we can write the default statement after the</div> <div> last case as under.</div> <div> default : cout << “Please enter grade from A to D or F ” ;</div> <div> The break statement is also used in decision structures other than switch structure. We</div> <div> have seen that in while, do-while and for loops, we have to violate some condition</div> <div> explicitly to terminate the loop before its complete repetitions. As in a program of</div> <div> guessing a character, we make a variable tryNum greater than 5 to violate the while</div> <div> condition and exit the loop if the correct character is guessed before five tries. In these</div> <div> loops, we can use the break statement to exit a loop. When a break statement is</div> <div> encountered in a loop, the loop terminates immediately. The control exits the inner</div> <div> most loop if there are nested loops. The control passes to the statement after the loop.</div> <div> In the guessing character example, we want that if the character is guessed in first or</div> <div> second attempt,. then we print the message ‘Congratulations, You guess is correct’</div> <div> and exit the loop. We can do this by using a break statement with an if statement. If</div> <div> the character is guessed, we print the message. Afterwards, the break statement is</div> <div> executed and the loop terminates. So we can write this as follows.</div> <div> if ( c == ‘z’ ) // c is input from user</div> <div> {</div> <div> cout << “Great, Your guess is correct” ;</div> <div> break;</div> <div> }</div> <div> Thus, break statement can be used to jump out of a loop very quickly.</div> <div> The flow chart of the switch statement is similar to if statement and is given below.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 70</div> <div> switch</div> <div> (variable )</div> <div> Process</div> <div> Process</div> <div> case const 1</div> <div> case const2</div> <div> break</div> <div> break</div> <div> The flow chart of switch statement</div> <div> The number of case statement can vary from</div> <div> 1 to any number. Thus there are same</div> <div> number of process blocks as cases.</div> <div> Now we can write the complete code for the program that prints the description of the</div> <div> grade entered by the user.</div> <div> The flow chart of the program is given below.</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 71</div> <div> Start</div> <div> switch (grade)</div> <div> Stop</div> <div> Display "Excellent"</div> <div> case 'A'</div> <div> break</div> <div> Display</div> <div> "Very Good"</div> <div> case 'B'</div> <div> break</div> <div> Display "Good"</div> <div> case 'C'</div> <div> break</div> <div> Display "Poor"</div> <div> case 'D'</div> <div> break</div> <div> Display "Fail"</div> <div> case 'F'</div> <div> break</div> <div> Display " Please</div> <div> enter grade A-D or</div> <div> F"</div> <div> default</div> <div> break</div> <div> The flow chart of a program that displays the description of a grade</div> <div> using switch statement</div> <div> The code of the program is given below.</div> <div> //This program gets a grade from user and displays a description accordingly</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 72</div> <div> # include <iostream.h></div> <div> main ( )</div> <div> {</div> <div> char grade ;</div> <div> cout << “Please enter the student’s grade : ” ;</div> <div> cin >> grade ;</div> <div> switch ( grade )</div> <div> {</div> <div> case ‘A’ : // grade was upper case A</div> <div> case ‘a’ : // grade was lower case a</div> <div> cout << “Excellent” ;</div> <div> break : // necessary to exit switch</div> <div> case ‘B’ : // grade was upper case B</div> <div> case ‘b’ : // grade was lower case b</div> <div> cout << “Very Good” ;</div> <div> break : // necessary to exit switch</div> <div> case ‘C’ : // grade was upper case C</div> <div> case ‘c’ : // grade was lower case c</div> <div> cout << “Good” ;</div> <div> break : // necessary to exit switch</div> <div> case ‘D’ : // grade was upper case D</div> <div> case ‘d’ : // grade was lower case d</div> <div> cout << “Poor” ;</div> <div> break : // necessary to exit switch</div> <div> case ‘F’ : // grade was upper case F</div> <div> case ‘f’ : // grade was lower case f</div> <div> cout << “Fail” ;</div> <div> break : // necessary to exit switch</div> <div> default :</div> <div> cout << “Please enter grade from A to D or F ” ;</div> <div> }</div> <div> }</div> <div> A sample out put of the program is shown here.</div> <div> Please enter the student’s grade : b</div> <div> Very Good</div> <div> continue Statement</div> <div> There is another statement relating to loops. This is the continue statement.</div> <div> Sometimes we have a lot of code in the body of a loop. The early part of this code is</div> <div> common that is to be executed every time (i.e. in every iteration of loop) and the</div> <div> remaining portion is to be executed in certain cases and may not be executed in other</div> <div> cases. But the loop should be continuous. For this purpose, we use the continue</div> <div> statement. Like the break statement, the continue statement is written in a single line.</div> <div> We write it as</div> <div> continue ;</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 73</div> <div> The continue forces the immediate next iteration of the loop. So the statements of the</div> <div> loop body after continue are not executed. The loop starts from the next iteration</div> <div> when a continue statement is encountered in the body of a loop. One can witness very</div> <div> subtle things while using continue.</div> <div> Consider the while loop. In while loop, we change the value of the variable of while</div> <div> condition so that it could make the condition false to exit the loop. Otherwise, the</div> <div> loop will become an infinite one. We should be very careful about the logic of the</div> <div> program while using continue in a loop. Before the continue statement, it is necessary</div> <div> to change (increment/decrement) the value of the variable on which the while</div> <div> condition depends. Similarly it is same with the do-while loop. Be careful to</div> <div> increment or decrement the conditional variable before the continue statement.</div> <div> In for loop, there is a difference. In a while loop when continue is encountered, the</div> <div> control goes to the while statement and the condition is checked. If condition is true</div> <div> the loop is executed again else the loop exits. In a for loop, the three things i.e.</div> <div> initialization, condition and increment/decrement are enclosed together as we write</div> <div> for ( counter = 0 ; counter <= 5 ; counter ++) . In the for loop when a continue is</div> <div> encountered, the counter (i.e. loop variable) is incremented at first before the</div> <div> execution of the loop condition. Thus, in 'for loop' the increment to the loop variable</div> <div> is built in and after continue the next iteration of the loop is executed by incrementing</div> <div> the loop variable. The condition is checked with the incremented value of the loop</div> <div> variable. In while and do-while loop, it is our responsibility to increment the value of</div> <div> the loop variable to test the condition. In a for loop, the continue automatically forces</div> <div> this increment of value before going to check the condition.</div> <div> goto Statement</div> <div> Up to now we have covered the basic programming constructs. These include</div> <div> sequences, decisions and repetition structures (i.e. loops). In sequences, we use the</div> <div> simple statements in a sequence i.e. one after the other. In decisions construct we use</div> <div> the if statement, if/else statement, the multi way decision construct (i.e. the switch</div> <div> statement). And in repetition structures, we use the while, do-while and for loops.</div> <div> Sometime ago, two computer scientists Gome and Jacopi proved that any program</div> <div> can be written with the help of these three constructs (i.e. sequences, decisions and</div> <div> loops).</div> <div> There is a statement in the computer languages COBOL, FORTRON and C. This</div> <div> statement is goto statement. The goto is an unconditional branch of execution. The</div> <div> goto statement is used to jump the control anywhere (back and forth) in a program. In</div> <div> legacy programming, the programs written in COBOL and FORTRAN languages</div> <div> have many unconditional branches of execution. To understand and decode such</div> <div> programs that contain unconditional branches is almost impossible. In such programs,</div> <div> it is very difficult, for a programmer, to keep the track of execution as the control</div> <div> jumps from one place to the other and from there to anywhere else. We call this kind</div> <div> of traditional code as spagatti code. It is very difficult to trace out the way of</div> <div> execution and figure out what the program is doing. And debugging and modifying</div> <div> such programs is very difficult.</div> <div> When structured programming was started, it was urged not to use the goto statement.</div> <div> Though goto is there in C language but we will not use it in our programs. We will</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 74</div> <div> adopt the structured approach. All of our programs will consist of sequences,</div> <div> decisions and loops.</div> <div> Guide Lines</div> <div> In general, we should minimize the use of break statement in loops. The switch</div> <div> statement is an exception in this regard where it is necessary to use the break</div> <div> statement after every case. Otherwise, there may be a logical error. While writing</div> <div> loops, we should try to execute the loops with the condition test and should try to</div> <div> avoid the break statement. The same applies to the continue statement. The continue</div> <div> statement executes some statements of the loop and then exits the loop without</div> <div> executing some statements after it. We can use the if statement for this purpose</div> <div> instead of continue. So never use the goto statement and minimize the usage of break</div> <div> and continue statements in loops. This will make the code easy to understand for you</div> <div> and for others. Moreover the additions and modifications to such code will be easy, as</div> <div> the path of execution will be easy to trace.</div> <div> Make a program modular. This means that divide a large program into small parts. It</div> <div> will be easy to manage these small parts rather than a larger program. There should be</div> <div> single entry and single exit in every module or construct. The use of break statement</div> <div> in a construct violates this rule as a loop having a break statement can exit through</div> <div> break statement or can terminate when the loop condition violates. As there are two</div> <div> exit points, this should be avoided. The single entry- single exit approach makes the</div> <div> execution flow simple.</div> <div> Here is an example from daily life, which shows that single entry and single exit</div> <div> makes things easy. You would have often seen at a bus stop, especially in rush hours,</div> <div> that when a bus reaches the stop, everyone tries to jump into the bus without caring</div> <div> for others. The passengers inside the bus try to get down from the vehicle. So you see</div> <div> there a wrestling like situation at the door of the bus. Separate doors for entering or</div> <div> exiting the bus can be the solution. In this way, the passengers will easily enter or exit</div> <div> the bus.</div> <div> We have applied this single entry and single exit rule in drawing our flow charts. In</div> <div> the flow charts, we draw a vertical line from top to down. The point where the line</div> <div> starts is our entry point and downward at the same line at the end is our exit point.</div> <div> Our all other processes and loops are along or within these two points. Thus our flow</div> <div> charts resemble with the code.</div> <div> Rules for Structured Programming/Flow Charting</div> <div> There are few simple rules for drawing structured flow charts of programs. One</div> <div> should be familiar with these.</div> <div> Rule No:1-Start with the simple flow chart. This means that draw a start symbol,</div> <div> draw a rectangle and write in it whatsoever you want to do and then draw a stop</div> <div> symbol. This is the simplest flow chart.</div> <div> Rule No:2- Any rectangle ( a rectangle represents a process which could be input,</div> <div> output or any other process) can be replaced by two rectangles.</div> <div> This concept is the same as taking a complex problem and splitting it up into two</div> <div> simpler problems. So we have ‘split it up’ method to move towards a modular</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 75</div> <div> approach. So start with a block (rectangle) and then any rectangle can be replaced by</div> <div> two rectangles (blocks).</div> <div> Rule No:3- Any rectangle can be replaced with a structured flow charting construct.</div> <div> These construct include decisions, loops or multi- way decision. This means that we</div> <div> can put a structure of an if construct or switch construct in the place of a rectangle.</div> <div> Here we come to know the advantage of single entry and single exit concept. This</div> <div> single entry and single exit block can be replaced with a rectangle.</div> <div> Rule No: 4- This rule states that rule number 2 and 3 can be repeated as many times</div> <div> as you want.</div> <div> By using these rules we are splitting a problem into simpler units so that each part can</div> <div> be handled either by sequences (one rectangle, second rectangle and so on) or by a</div> <div> decision (if, if/else, switch or by a loop). Through this approach, a large problem can</div> <div> be solved easily.</div> <div> The flow charts drawn with these rules and indented to the left side will have one to</div> <div> one correspondence with our code. Thus it becomes very easy to identify the code that</div> <div> is written for a specific part of the flow chart. In this way the code can easily be</div> <div> debugged.</div> <div> Sample Program</div> <div> Let’s consider a problem. In a company, there are deductions from the salary of the</div> <div> employees for a fund. The deductions rules are as follows:</div> <div> If salary is less than 10,000 then no deduction</div> <div> If salary is more than 10,000 and less than 20,000 then deduct Rs. 1,000 as fund</div> <div> If salary is equal to or more than 20,000 then deduct 7 % of the salary for fund</div> <div> Take salary input from user and after appropriate deduction show the net payable</div> <div> amount.</div> <div> Solution</div> <div> As we see that there is multi way decision in this problem, so we use switch</div> <div> statement. The salary is the switch variable upon which the different decisions</div> <div> depend. We can use only a single constant in case statement. So we divide the salary</div> <div> by 10000 to convert it into a single case constant. As we know that in integer division</div> <div> we get the whole number as the answer. Thus if answer is 0 the salary is less than</div> <div> 10000, if answer is 1 then it is in range 10000 to 19999 ( as any amount between</div> <div> 10000 – 19999 divided by 10000 will result 1). If the answer is greater than 1, it</div> <div> means the salary is equal to or more than 20000.</div> <div> Following is the complete code of our program.</div> <div> // This program gets salary input from user and calculates and displays the net payable</div> <div> // amount after deduction according the conditions</div> <div> # include <iostream.h></div> <div> main ( )</div> <div> {</div> <div> int salary ;</div> <div> float deduction, netPayable ;</div> <div> cout << “Please enter the salary : “ ;</div> <div> cin >> salary ;</div> <div> // here begins the switch statement</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 76</div> <div> switch ( salary / 10000 ) // this will produce a single value</div> <div> {</div> <div> case 0 : // this means salary is less than 10,000</div> <div> deduction = 0; // as deduction is zero in this case</div> <div> netPayable = salary ;</div> <div> cout << “Net Payable (salary – deduction) = “ ;</div> <div> cout << salary << “ - ” << deduction << “ = “ << netPayable;</div> <div> break; //necessary to exit switch</div> <div> case 1 : // this means salary is in range 10,000 – 19,999</div> <div> deduction = 1000 ;</div> <div> netPayable = salary – deduction ;</div> <div> cout << “Net Payable (salary – deduction) = “ ;</div> <div> cout << salary << “ - ” << deduction << “ = “ << netPayable;</div> <div> break; //necessary to exit switch</div> <div> default : // this means the salary is 20,000 or more</div> <div> deduction = salary * 7 /100 ;</div> <div> netPayable = salary – deduction ;</div> <div> cout << “Net Payable (salary – deduction) = “ ;</div> <div> cout << salary << “ - ” << deduction << “ = “ << netPayable;</div> <div> }</div> <div> }</div> <div> Here is the out put of the program.</div> <div> Please enter the salary : 15000</div> <div> Net Payable (salary – deduction) = 15000 – 1000 = 14000</div> <div> Tips</div> <div> Try to use the switch statement instead of multiple if statements</div> <div> Missing a break statement in a switch statement may cause a logical error</div> <div> Always provide a default case in switch statements</div> <div> Never use goto statement in your programs</div> <div> Minimize the use of break and continue statements</div> <div> CS201 – Introduction to Programming</div> <div> © Copyright Virtual University of Pakistan</div> <div> 77</div> <div> Lecture No. 9</div> <div> Reading Material</div> <div> Deitel & Deitel – C++ How to Program chapter 2</div> <div> 3.1, 3.2, 3.3, 3.4,</div> <div> 3.5, 3.6</div> <div> Summary</div> <div> o Introduction</div> <div> o Functions</div> <div> o Structure of a Function</div> <div> o Declaration and Definition of a Function</div> <div> o Sample Program 1</div> <div> o Sample Program 2</div> <div> o Sample Program 3</div> <div> o Summary</div> <div> o Tips</div> <div> Introduction</div> <div> Now our toolkit is almost complete. The basic constructs of programming are</div> <div> sequence, decision making and loops. You have learnt all these techniques. Now we</div> <div> can write almost all kinds of programs. There are more techniques to further refine the</div> <div> programs. One of the major programming constructs is Functions. C is a functionoriented</div> <div> language. Every program is written in different functions.</div> <div> In our daily life, we divide our tasks into sub tasks. Consider the making of a</div> <div> laboratory stool.</div> </div> <div> <br /></div> <div> <b><span style="font-size: large;">Download Book</span></b></div> <div> <b><span style="font-size: large;"><a href="http://www.genrica.com/vustuff/CS201/CS201_handouts_1_45.pdf" target="_blank">Introduction to Programming CS201 book HANDOUTS in pdf</a></span></b></div>

Introduction to Programming CS201 book HANDOUTS in pdf

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