C Comments: The Complete Beginner’s Guide

Comments in C are used to explain code, make it readable, and debug programs. They are ignored by the compiler, so they don’t affect the program’s output.

Think of comments as notes to yourself or other developers.

Types of Comments in C

C supports two types of comments:

Single-line Comment

Use // before the comment.

// This is a single-line comment
printf("Hello, World!\n");  // This prints text

Multi-line Comment

Use /* */ to write comments that span multiple lines.

/* 
   This is a multi-line comment.
   It can span multiple lines.
*/
printf("Welcome to C!\n");

Example Program with Comments

#include <stdio.h>

int main() {
    // Declare a variable
    int age = 25;

    /* Display the age */
    printf("Age: %d\n", age);

    return 0; // End of the program
}

Output:

Why Use Comments in C?

Purpose	Example
Explain complex logic	`// Loop to check prime number`
Disable code temporarily	`// printf("Debug info");`
Improve collaboration	`/* TODO: Add error handling here */`

Best Practices for Using Comments

Write comments only where necessary

Keep them short and meaningful

Update comments when code changes

Avoid obvious comments like // Print hello right above printf("Hello");

Use TODO and FIXME for tracking tasks

Common Mistakes to Avoid

Mistake	Correct Way
Using nested multi-line comments	Not allowed in C
Writing unnecessary or redundant comments	Only comment when it adds value
Using `'` instead of `"` in strings	Not a comment issue, but common confusion
Forgetting to close multi-line comments	Use `*/` to end the comment