Comments

Part of the Fundamentals section of Coddy's C journey — lesson 3 of 63.

Comments are notes you write inside your code. The compiler completely ignores them - they exist only to help humans understand the code.

To write a single-line comment, use //. Everything after // until the end of the line is ignored:

// This is a comment
printf("Hello, World!");

A comment can also be written at the end of a line, after the code:

printf("Hello, World!"); // This prints Hello, World!

For comments that span several lines, use /* to start and */ to end:

/* This is a multi-line comment.
   The compiler ignores all of it. */
printf("Welcome!");

Comments can also temporarily disable a line of code without deleting it:

// printf("This line will NOT run");
printf("This line will run");

Challenge

Beginner

Fix the code so that only Hello, C! is printed.

Cheat sheet

Comments in C:

Single-line comment:

// This is a comment
printf("Hello!"); // Comment after code

Multi-line comment:

/* This is a
   multi-line comment */

Disabling code:

// printf("This will NOT run");
printf("This will run");

Try it yourself

#include <stdio.h>

int main() {
    // Type your code below
    ? printf("Goodbye!\n");
    printf("Hello, C!\n");

    return 0;
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

1Introduction

4Control Flow

7Functions