C++ Comments

Single-Line Comments

Single-line comments start with two forward slashes //. Everything after // on that line is ignored by the compiler.

// This is a single-line comment
cout << "Hello World!"; // This comment is at end of a statement

Multi-Line Comments

Multi-line comments start with /* and end with */. They can span multiple lines.

/* This is a multi-line comment.
   It can span many lines.
   The compiler ignores everything between the delimiters. */
cout << "Comments don't affect output!";

Full Example

#include <iostream>
using namespace std;

int main() {
    // Print a greeting message
    cout << "Hello!" << endl;

    /* This block demonstrates
       multi-line comments */
    cout << "Comments are for humans, not compilers." << endl;

    return 0; // End of program
}

Output:

Hello!
Comments are for humans, not compilers.

When to Use Comments

• Explain complex logic that is not obvious from the code.
• Temporarily disable code during debugging.
• Document functions — what they do, parameters, return values.
• Leave TODOs for future improvements.

#include <iostream>
using namespace std;

int main() {
    cout << "Name: Alex" << endl;
    cout << "Age: 25" << endl;
    return 0;
}

#include <iostream>
using namespace std;

int main() {
    // Print the user's name
    cout << "Name: Alex" << endl;
    // Print the user's age
    cout << "Age: 25" << endl;
    return 0;
}

Summary

• Use // for single-line comments.
• Use /* ... */ for multi-line comments.
• Comments are ignored by the compiler.
• Use comments to explain why, not what.