C Comments

Summary: in this tutorial, you will learn about C comments and how to use them to document your code.

Introduction to the C comments

A comment is an annotation in the source code. Typically, you use a comment to make the code easier to understand. In C, a comment starts with a slash followed by an asterisk (/*) and ends with an asterisk followed by a slash (*/). For example:

#include <stdio.h>

int main()
{
    /* counter always starts at 0 */
    int counter = 0;

    return 0;
}
Code language: C++ (cpp)

In this example, the following line is a comment:

/* counter always starts at 0 */
Code language: C++ (cpp)

When the C compiler compiles the program, it ignores all the comments.

A comment can be on the same line with the code as follows:

#include <stdio.h>

int main()
{
    int counter = 0; /* counter always starts at 0 */
    return 0;
}
Code language: C++ (cpp)

When the comment is on the same line as the code, it is called an inline comment.

C allows a comment to span multiple lines as shown in the following example:

/*
   This is an example of 
   a multi-line comment.
*/
Code language: C++ (cpp)

This is called a multi-line comment.

C99 inline comments

C99 allows you to write an inline comment that starts with two forward slashes (//). Everything after the two forward slashes belongs to the inline comment. For example:

#include <stdio.h>

int main()
{
    int counter = 0; // counter always starts at 0.
    return 0;
}
Code language: C++ (cpp)

In this example, the text counter always starts at 0. is the inline comment.

Summary

• Do use comments to add notes to your code to make it more clear.
• A comment starts with a slash followed by an asterisk (/*) and ends with an asterisk followed by a slash (*/).
• Use double slashes (//) to start an inline comment.
• C compilers ignore the comments when compiling the code.
• Do use clear and concise comments to document your code.