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This chapter is from the book

This chapter is from the book


The final program in this chapter (Program 3.6) introduces the concept of the comment. A comment statement is used in a program to document a program and to enhance its readability. As you will see from the following example, comments serve to tell the reader of the program—the programmer or someone else whose responsibility it is to maintain the program—just what the programmer had in mind when he or she wrote a particular program or a particular sequence of statements.

Program 3.6 Using Comments in a Program

/* This program adds two integer values 
  and displays the results       */

#include <stdio.h>

int main (void)
  // Declare variables 
  int value1, value2, sum;

  // Assign values and calculate their sum 
  value1 = 50;
  value2 = 25;
  sum = value1 + value2;

  // Display the result 
  printf ("The sum of %i and %i is %i\n", value1, value2, sum);

  return 0;

Program 3.6 Output

The sum of 50 and 25 is 75

There are two ways to insert comments into a C program. A comment can be initiated by the two characters / and *. This marks the beginning of the comment. These types of comments have to be terminated. To end the comment, the characters * and / are used without any embedded spaces. All characters included between the opening /* and the closing */ are treated as part of the comment statement and are ignored by the C compiler. This form of comment is often used when comments span several lines in the program. The second way to add a comment to your program is by using two consecutive slash characters //. Any characters that follow these slashes up to the end of the line are ignored by the compiler.

In Program 3.6, four separate comment statements were used. This program is otherwise identical to Program 3.5. Admittedly, this is a contrived example because only the first comment at the head of the program is useful. (Yes, it is possible to insert so many comments into a program that the readability of the program is actually degraded instead of improved!)

The intelligent use of comment statements inside a program cannot be overemphasized. Many times, a programmer returns to a program that he coded perhaps only six months ago, only to discover to his dismay that he could not for the life of him remember the purpose of a particular routine or of a particular group of statements. A simple comment statement judiciously inserted at that particular point in the program might have saved a significant amount of time otherwise wasted on rethinking the logic of the routine or set of statements.

It is a good idea to get into the habit of inserting comment statements into the program as the program is being written or typed in. There are good reasons for this. First, it is far easier to document the program while the particular program logic is still fresh in your mind than it is to go back and rethink the logic after the program has been completed. Second, by inserting comments into the program at such an early stage of the game, you get to reap the benefits of the comments during the debug phase, when program logic errors are being isolated and debugged. A comment can not only help you read through the program, but it can also help point the way to the source of the logic mistake. Finally, I have yet to discover a programmer who actually enjoyed documenting a program. In fact, after you have finished debugging your program, you will probably not relish the idea of going back to the program to insert comments. Inserting comments while developing the program makes this sometimes tedious task a bit easier to swallow.

This concludes this introductory chapter on developing programs in C. By now, you should have a good feel as to what is involved in writing a program in C, and you should be able to develop a small program on your own. In the next chapter, you begin to learn some of the finer intricacies of this wonderfully powerful and flexible programming language. But first, try your hand at the following exercises to make certain you understand the concepts presented in this chapter.

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