C++ Comments

In this tutorial, you’ll learn about C++ Comments, Single Line Comments, Multi-line comments, Using Comments for Debugging, and more.

Writing code is more than just telling a computer what to do. It’s also about communicating your intentions and logic to other developers (including your future self!). This is where comments in C++ come in.

What are C++ Comments?

C++ comments are annotations within the source code that are disregarded by the compiler. They’re designed solely for human readers, providing explanations, context, and documentation directly within the code itself.

#include <iostream>
using namespace std;

int main() {
    // print Hello World to the screen
    cout << "Hello World";

    return 0;
}

Single-Line Comments

Single-line comments are used for short, concise explanations on a single line of code. They begin with two forward slashes (//). Everything after the slashes on that line is treated as a comment and ignored by the compiler.

#include <iostream>

int main() {
  int age = 25; // Declare an integer variable named age and initialize it to 25.
  std::cout << "Age: " << age << std::endl; // Output the value of age to the console.
  return 0; // Return 0 to indicate successful program execution.
}

Multi-Line Comments

Multi-line comments, also known as block comments, are used for longer explanations that span multiple lines. They begin with /* and end with */. Everything between these markers is treated as a comment.

#include <iostream>

/*
This is a multi-line comment.
It can span multiple lines and is useful for
providing more detailed explanations or
documenting larger sections of code.
*/

int main() {
  int radius = 5;
  double area;

  // Calculate the area of a circle.
  area = 3.14159 * radius * radius;

  std::cout << "Area: " << area << std::endl;
  return 0;
}

Using Comments for Debugging

Comments can be a powerful debugging tool. You can temporarily “comment out” sections of code to isolate problems. If you suspect a particular block of code is causing a bug, you can comment it out and run the program again. This helps you narrow down the source of the error.

#include <iostream>

int main() {
  int x = 10;
  int y = 0;
  int result;

  // result = x / y;  // Potential division by zero error! Commented out for debugging.
  result = x * 2;   // Testing a different calculation.

  std::cout << "Result: " << result << std::endl;
  return 0;
}

In this example, the division operation is commented out because it could lead to a division by zero error. This allows the programmer to test other parts of the code without encountering the error. Once the bug is fixed, the comment can be removed.

Why Use Comments?

Comments are essential for writing maintainable and understandable code. Here’s why:

• Improved Readability: Comments make your code easier to read and understand, especially when dealing with complex logic.
• Documentation: Comments serve as a form of documentation, explaining the purpose and functionality of different parts of your code.
• Debugging Aid: Comments can be used to temporarily disable code during debugging, helping you isolate and fix errors.
• Code Maintenance: Well-commented code is easier to maintain and modify. When you need to make changes, comments help you understand the existing code, reducing the risk of introducing new bugs.
• Collaboration: Comments facilitate collaboration among developers by making the code easier to understand and share.