Comments in C

Comments add explanations for people reading source code. They are not executable C statements. Use // for a comment that continues to the end of the line, or /* ... */ for a block comment.

Single-Line Comments Top ↑

int num = 10;  // Store an integer value

// Display the value
printf("%d\n", num);

Everything after // on that source line is part of the comment.

Block Comments Top ↑

/* This is a block comment.
   It can continue across
   multiple source lines. */

Comments Inside a Working Program Top ↑

#include <stdio.h>

int main(void) {
    double number = 17.873;  // Declare and initialize

    /* Display the value with
       three digits after the decimal point. */
    printf("number = %.3f\n", number);
    return 0;
}

Output

number = 17.873

Avoid Nested Block Comments Top ↑

Standard C block comments do not nest. This should not be used:

/* outer comment /* inner comment */ rest of text */

The first */ ends the block comment, leaving the remaining text to be parsed as source code.

Good Comment Practice Top ↑

• Explain why a non-obvious step is needed rather than repeating what the code already says.
• Keep comments synchronized when code changes.
• Do not use comments to hide large amounts of obsolete code in a finished tutorial example.

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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