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");

Note: Every multi-line comment that starts with /* must be closed with */, otherwise the compiler treats everything after it as a comment.

Challenge

Beginner

Turn the line that prints Goodbye! into a comment, so only Hello, C! is printed.

Add // in front of printf("Goodbye!\n"); on its line, so that line reads // printf("Goodbye!\n");
Don't add or delete lines

Try it yourself

#include <stdio.h>

int main() {
    // Type your code below
    // Add // in front of the Goodbye line below. Don't type a new line.
    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.

All lessons in Fundamentals

1Introduction

C Language Hello World!CommentsBasic Program Structure

4Control Flow

If Statement If - Else Else-If Switch Case Ternary Conditional Operator Recap Challenge Nested If - Else

7Functions

Declare a Function Return Types Parameters Recap Challenge #1 Recursion Basics Function Prototypes Recap Challenge #2

Practice on your own: Online C compiler