Comments

Comments are notes written by a programmer that are completely ignored by the C++ compiler. They exist purely for humans to read.

While the code itself tells you what the program is doing, comments are used to explain why. They can be used to:

• Clarify complex or tricky parts of your code.
• Leave reminders for yourself or notes for other programmers.
• Temporarily disable a line or block of code for testing, a process known as commenting out.

Good code doesn't need many comments, but when used wisely, they can be very helpful.

Single-line Comment

A single-line comment starts with // and continues to the end of the line.

#include <bits/stdc++.h>
using namespace std;

int main() {
    // This line prints a message to the console.
    cout << "Hello, World!" << endl;

    // The following line is disabled because it is commented out.
    // cout << "This will not be printed." << endl;

    return 0; // Return 0 to indicate success
}

Note that the // syntax does not work inside a string literal.

cout << "This is not a // comment" << endl;

The above code will print This is not a // comment to the console.

Multi-line Comment

A multi-line comment starts with /* and ends with */. Everything between these markers is ignored, even if it spans multiple lines.

This is useful for writing longer explanations or for commenting out large blocks of code.

#include <bits/stdc++.h>
using namespace std;

int main() {
    /*
      This is a multi-line comment.
      It can span across several lines.
      The code below calculates the area of a rectangle.
    */
    int score = 10;
    cout << "The score is: " << score << endl;

    /*
    cout << "This is a block of code that is commented out." << endl;
    score = 15;
    */

    cout << "The score is: " << score << endl; /* Outputs 10. */

    return 0;
}

Like the single-line comment, the /* */ syntax also does not work inside a string literal.

cout << "This is not a /* comment */" << endl;

The above code will print This is not a /* comment */ to the console.