PROGRAM CONTROL

THE WHILE LOOP

The C programming language has several structures for looping and conditional branching. We will cover them all in this chapter and we will begin with the while loop. The while loop continues to loop while some condition is true. When the condition becomes false, the looping is discontinued. It therefore does just what it says it does, the name of the loop being very descriptive. 

Example program ------> WHILE.C

Load the program WHILE.C and display it for an example of a while loop. We begin with a comment and the program entry point main(), then go on to define an integer variable named count within the body of the program. The variable is set to zero and we come to the while loop itself. The syntax of a while loop is just as shown here. The keyword while is followed by an expression of something in parentheses, followed by a compound statement bracketed by braces. As long as the expression in the parenthesis is true, all statements within the braces will be repeatedly executed. In this case, since the variable count is incremented by one every time the statements are executed, it will eventually reach 6. At that time the statement will not be executed because count is not less than 6, and the loop will be terminated. The program control will resume at the statement following the statements in braces.We will cover the compare expression, the one in parentheses, in the next chapter. Until then, simply accept the expressions for what you think they should do and you will be correct for these simple cases.

Several things must be pointed out regarding the while loop. First, if the variable count were initially set to any number greater than 5, the statements within the loop would not be executed at all, so it is possible to have a while loop that never is executed. Secondly, if the variable were not incremented in the loop, then in this case, the loop would never terminate, and the program would never complete. Finally, if there is only one statement to be executed within the loop, it does not need delimiting braces but can stand alone. Compile and run this program after you have studied it enough to assure yourself that you understand its operation completely. Note that the result of execution is given for this program, (and will be given for all of the remaining example programs in this tutorial) so you do not need to compile and execute every program to see the results. Be sure to compile and execute some of the programs however, to gain experience with your compiler. You should make some modifications to any programs that are not completely clear to you and compile them until you understand them completely. The best way to learn is to try various modifications yourself. We will continue to ignore the #include statement and the return statement in the example programs in this lesson. 

GOOD FORMATTING STYLE

GOOD FORMATTING STYLE

Example program ------> GOODFORM.C

Load the file GOODFORM.C and observe it on your monitor. It is an example of a well formatted

program. Even though it is very short and therefore does very little, it is very easy to see at a glance what it does. With the experience you have already gained in this tutorial, you should be able to very quickly grasp the meaning of the program in it's entirety. Your C compiler ignores all extra spaces and all carriage returns giving you considerable freedom in formatting your program. Indenting and adding spaces is entirely up to you and is a matter of personal taste. Compile and run the program to see if it does what you expect it to do.

Example program ------> UGLYFORM.C

Now load and display the program UGLYFORM.C and observe it. How long will it take you to figure out what this program will do? It doesn't matter to the compiler which format style you use, but it will matter to you when you try to debug your program. Compile this program and run it. You may be surprised to find that it is the same program as the last one, except for the formatting. Don't get too worried about formatting style yet. You will have plenty of time to develop a style of your own as you learn the C language. Be observant of styles as you see C programs in magazines and books. This covers some of the basic concepts of programming in C, but as there are many other things to learn, we will forge ahead to additional program structure. It will definitely be to your advantage to do the programming exercises at the end of each chapter. They are designed to augment your studies and teach you to use your compiler.