Comments

Big idea

A comment is a note for humans. The computer skips it completely.

The idea

Comments explain why your code does something — for someone reading it later (often future you). They never change what the program does.

C has two kinds:

• // — a comment until the end of the line.
• /* ... */ — a comment that can cover many lines.

Example

#include <stdio.h>

int main(void) {
    // This line says hello
    printf("Hello\n");

    /* This whole block
       is ignored too */
    return 0;
}

output
Hello

Only Hello is printed. Both comments are skipped.

Watch it

Think of it like

Sticky notes on a recipe. The cook reads them, but they aren't cooking steps.

🕷️ Spidey-sense: Comments are the sticky notes I leave on my web-shooters for future me. The computer skips them completely — they're only for humans. Write why you did something, not just what.

Common mistake

Forgetting to close a block comment. Everything after /* stays a comment until */ — even your real code.

Key terms

• Comment — A note in code that the compiler ignores.
• // — Starts a single-line comment.
• /* */ — Wraps a multi-line comment.