Overview

Comments serve as the unsung heroes of code. They provide clarity, documentation, and organization to your programs. In this chapter, we will explore the importance of comments in C++, various types of comments, and best practices for using them effectively.

Why Are Comments Important?

Comments are not just text; they are an integral part of your code. They serve several crucial purposes:

Explanation

Comments explain the purpose and functionality of code. They help both you, the programmer, and others who might read your code understand its logic.

// This function calculates the area of a rectangle.
double calculateRectangleArea(double length, double width) {
    return length * width;
}

Documentation

Comments provide documentation for your code, making it easier for others (or even yourself, months later) to use or modify it. Properly documented code saves time and reduces errors during maintenance.

Debugging

Comments can be used to temporarily remove sections of code during, debugging, a technique known as commenting out. This allows you to isolate and identify issues without deleting the code.

Commenting out: Converting one or more lines of code into a comment is called commenting out your code.

/* Debugging code
int buggyFunction() {
    // ...
}
*/

Tip: If you always use single line comments for your normal comments, then you can always use multi-line comments to comment out your code without conflict. If you use multi-line comments to document your code, then commenting-out code using comments can become more challenging. If you do need to comment out a code block that contains multi-line comments, you can also consider using the #if 0 preprocessor directive.

Types of Comments in C++

C++ offers several ways to add comments to your code, each with its own purpose and use case:

Single-Line Comments

Single-line comments start with // and continue until the end of the line. They are perfect for short explanations or comments on a single line of code.

// This is a single line comment
int age = 30; // This is also an single-line comment

std::cout << "Hello world!\n"; // std::cout lives in the iostream library
std::cout << "It is very nice to meet you!\n"; // these comments make the code hard to read
std::cout << "Yeah!\n"; // especially when lines are different lengths

• Having comments to the right of a line can both the code and comment hard to read, particularly if the line is long.
• Single-line comments are often placed above the line it is commenting.

// std::cout lives in the iostream library
std::cout << "Hello world!\n";

// this is much easier to read
std::cout << "It is very nice to meet you!\n";

Multi-Line Comments

Multi-line comments are enclosed between /* and */ and can span multiple lines. Everything in between the symbols is ignored. They are suitable for longer explanations or comments that span multiple lines of code.

/*
   This is a multi-line comment.
   It can span multiple lines.
*/

Since everything between the symbols is ignored, you will sometimes see programmers beautify their multi-line comments:

/* This is a multi-line comment.
 * the matching asterisks to the left
 * can make this easier to read
 */

Multi-line style comments can not be nested. Consequently, the following will have unexpected results:

/* This is a multi-line /* comment */ this is not inside the comment */
// The above comment ends at the first */, not the second */

Documentation Comments

Documentation comments, also known as Doxygen comments, are a special type of comment used to generate documentation from your code. They start with /// or /** and are commonly used for documenting functions, classes, and variables.

/// This is a documentation comment for a function.
int add(int a, int b) {
    return a + b;
}

Comment Best Practices

To harness the full power of comments in C++, consider the following best practices:

Be Clear and Concise

Comments should be clear and to the point. Avoid overly technical jargon and use plain language so that anyone can understand them.

Keep Comments Updated

As your code evolves, remember to update your comments to reflect any changes. Outdated comments can be misleading and counterproductive.

Avoid Over-commenting

While its essential to provide clarity, avoid excessive commenting. Code should be self-explanatory to a reasonable extent. Over-commenting can clutter your code and make it harder to read.

Use Documentation Tools

If you are developing libraries or APIs, consider using documentation tools like Doxygen or Javadoc to automatically generate documentation from specially formatted comments.

Conclusion

Comments in a programming language are your allies in writing clean, understandable, and maintainable code. They not only explain your code`s functionality but also serve as valuable documentation for yourself and other work with your code. By following best practices and using different types of comments effectively, you can significantly enhance the readability and longevity of your programs.