C++ Comments

C++ comments are like notes we scribble in the margins of our code, but unlike messy handwriting, these notes are perfectly ignored by the computer.

So, why bother with them? One word, readability.

Comments are like journals, turning complex code into a story that you and other developers can easily follow. Comments also make maintenance easier. Imagine revisiting our own code months later, comments are the memory joggers that help us understand our past decisions.

Also, like many other developers, I believe that comments help us pinpoint problems by temporarily 'switching off' sections of code for testing. Let us learn all about C++ comments.

What are Comments in C++?

C++ comments are sections of text within your code that the compiler intentionally ignores during the compilation process. They are designed specifically for human readers.

C++ inherited its commenting style directly from the C programming language, which is its predecessor. The concept of cpp comment has been around since the early days of programming languages. The value of explaining code for human understanding was quickly recognized.

Comments exist to enhance code readability, explain logic, and improve maintainability. They serve as notes for yourself and other developers. Commenting syntax is now standardized, ensuring that comments written in C++ will be interpreted correctly by C++ compilers across different systems.

Why C++ Comments Matter

Here are three key reasons why C++ comments matter:

• Collaboration: Projects often involve multiple developers; comments aid knowledge sharing and understanding.
• Long-term maintenance: Well-commented code is much easier to revisit and modify, even months or years later.
• Debugging: Comments can help isolate issues by temporarily deactivating code sections.
• Learning: Comments in examples or tutorials can clarify concepts for those learning C++.

Types of C++ Comments

There are two types of C++ comments. Let us learn about them.

Single Line Comment in C++ (//)

The double-slash (//) marks the beginning of a single-line comment. Everything from the // to the end of the line is disregarded by the compiler.

Example:

int age = 25; // This variable stores the person's age
// Calculate discount based on age
if (age > 60) {
discount = 0.15; // 15% discount for seniors
}

Single line comment in C++ is used for:

• Brief notes: Adding quick explanations next to lines of code.
• Labels: Marking specific sections of code for easy reference.
• Temporary code deactivation: "Commenting out" code for testing or debugging purposes.

Multi Line Comment in C++ (/**/)

A multi-line comment begins with /* and ends with */. Everything enclosed within these markers is ignored, regardless of how many lines it spans. Multi-line comments (/* */) cannot be nested within each other and attempting to do so may lead to compiler errors.

Example:

/*
This function calculates the factorial of a given number.
Factorial of n is defined as n! = n * (n-1) * (n-2) * ... * 1
*/
int calculateFactorial(int n) {
// ... code here ...
}

Multi line comment in C++ is used for:

• Complex descriptions: Providing in-depth explanations for functions, data structures, or algorithms.
• Outlining steps: Breaking down a longer process into commented steps.
• Commenting out large sections: Temporarily deactivating blocks of code for testing or modification.

C++ How to Comment Strategically

The key to effective commenting lies in understanding when it's truly beneficial and when it's just code clutter. Let us learn more about properly using the C++ comment line.

When to Comment

Here are some situations where you should use the C++ comment line:

• Non-obvious logic: If your code performs complex calculations, uses tricky algorithms, or has non-intuitive side effects, explain the underlying thought process.
• Purpose and intent: Clarify the reason behind a function, a variable, or a specific code choice, especially if it might not be immediately clear.
• External dependencies: If your code relies on specific libraries, hardware, or system configurations, mention them in comments.

When Not to Comment

Here are some situations where you should not use the C++ comment line:

• The obvious: Don't explain what the code itself already makes clear (e.g., int x = 5; // Assign 5 to variable x).
• Redundancy: Avoid comments that merely restate the code in plain English.
• Over-commenting: Too many comments can be as distracting as too few. Strike a balance.

Clarity and Conciseness in C++ Comments

Here is how we can maintain clarity and conciseness in C++ comments:

• Simple language: Use clear and understandable language; avoid overly technical jargon unless your audience is well-versed.
• To the point: Express your ideas in the most concise way possible. Avoid long, rambling comments.
• Formatting: Use spacing and indentation to make multi-line comments easier to read.

Commenting for Collaboration

In team development environments, C++ comments become a vital communication tool:

• Knowledge sharing: Thorough comments help new team members or those onboarding to a project get up to speed quickly.
• Change tracking: Use comments to explain modifications to the code, the reasoning behind them, and who made the change.
• Code reviews: Comments become focal points for discussion and feedback during code reviews.
• Task assignment: Comments can sometimes act as simple "to-do" markers for unfinished sections of code.

In-Depth Tips for Team Commenting

Here are some tips for team commenting:

• Agree on conventions: Establish commenting standards within your team (level of detail, style, etc.) to maintain consistency.
• Version control integration: Comments tied to version control commits provide context for why changes were made.
• Blame without shame: Focus on commenting for clarity and understanding, not finger-pointing when code issues are uncovered.

Shortcuts for C++ Comments

Looking for how to comment in C++ shortcut? Here are the shortcuts for C++ comments:

Single-line Comment

• Windows/Linux (most editors): Ctrl + /
• macOS (most editors): Cmd + /

Multi-line Comment (Toggle)

• Windows/Linux (most editors): Ctrl + Shift + /
• macOS (most editors): Cmd + Shift + /

I want to mention that some code editors (like Visual Studio) might have slightly different shortcuts or additional options for commenting. We should always check our editor's documentation if unsure. Also, many editors allow us to customize keyboard shortcuts to our preference.

C++ Comments Advanced Techniques

Let us discuss some advanced commenting techniques that go beyond basic comments.

Commenting for Debugging

When you encounter a bug, use comments to disable sections of your code one by one. This helps narrow down where the issue lies. Comment out code blocks to test alternative implementations or temporarily disable features to see how it affects the overall program.

Example:

//calculateDiscount(price, age); // Original code
price = price * 0.9; // Bypass the calculation temporarily for testing

Conditional Compilation (with C++ Comments)

Preprocessor directives (#ifdef, #ifndef, #else, #endif) allow you to include or exclude code blocks based on conditions defined during compilation. Comments can also be used in conjunction to explain the reasoning behind conditional sections.

Example:

#ifdef DEBUG // If the 'DEBUG' symbol is defined during compilation
// cout << "Debugging information: " << var << endl; // Print debug output
#endif

Doxygen

Doxygen is a popular tool that can parse specially formatted comments within your code to automatically generate clear and organized documentation. Doxygen-style comments use specific tags (e.g., @brief, @param, @return) to describe functions, parameters, and more. While Doxygen leverages comments, it's a powerful tool that creates professional-level documentation for your projects.

Comments in C++ Example

Here is an example of C++ comments:

#include <iostream>
int main() {
int numApples = 10; // Number of apples in the basket
int numOranges = 5; // Number of oranges in the basket
int totalFruits = numApples + numOranges;
std::cout << "Total number of fruits: " << totalFruits << std::endl;
return 0;
}

If you wish to learn how to code in C++, you can check out upGrad’s software engineering courses.

Good Commenting Habits

Let us discuss a few solid commenting habits.

Regular Updates

• Comments and code are partners: As you modify your code, make sure to update any corresponding comments. Outdated comments can be more misleading than no comments at all.
• Change tracking: If a comment is made obsolete by a code change, briefly explain why it was once necessary. This adds historical context for future developers.
• Preemptive for major changes: If you anticipate large code revisions, add comments to flag areas most likely to be affected, aiding future updates.

Code Reviews

• Focal points for discussion: Use comments to highlight specific code sections that might require extra scrutiny or questions during code reviews.
• Alternative implementations: If you have an alternative approach you considered but didn't implement, leave it as a commented-out section with an explanation of why you made your final choice.
• Ownership: Sign changes with your initials or name within comments, especially in larger team projects. This promotes accountability and helps trace back the thought process.

Additional Tips for Fostering Good Habits

• Version control: Comments, when coupled with commit messages, provide a powerful history of your project's evolution and decisions.
• Team standards: Establish team-wide commenting guidelines for consistency and ease of collaboration.

Bad vs. Good Comments

Bad: The Obvious

Example:

int x = 5; // Assign the value 5 to the variable x

Why it's bad: This comment merely restates what the code itself does.

Good: Explaining Intent

Example:

int maxAttempts = 3; // Maximum number of login retries before lockout

Why it's good: Clarifies the purpose behind the value choice.

Bad: Overly Long

Example:

// This function calculates the area of a rectangle by taking
// the length and the width as inputs, multiplying them together,
// and then returning the result of the multiplication.
double calculateArea(double length, double width) {
// ...
}

Why it's bad: The comment is long and adds little value beyond what the code itself and function name convey.

Good: Concise and Informative

Example:

// Assumes length and width are non-negative values.
double calculateArea(double length, double width) {
// ...
}

Why it's good: Provides a crucial assumption about the function's inputs

Commenting Challenge

Here is a task for you. Check the code below and add comments to explain the logic behind the discount calculation. Also, consider where additional clarifications might be helpful.

double calculateDiscount(double originalPrice, int customerAge, bool isMember) {
double discount = 0.0;
if (customerAge > 65) {
discount = 0.15; // Senior discount
}
if (isMember) {
discount += 0.05; // Member discount
}
if (originalPrice > 50 && discount == 0) {
discount = 0.02; // Courtesy discount for larger purchases
}
return originalPrice * (1 - discount);
}

Final Tips

While it might seem like an additional step during the coding process, investing time in writing clear and purposeful comments pays incredible dividends in the long run. Comments capture our thought processes and decisions, preventing them from being lost as time passes or as teams change. Modifying or expanding well-commented code becomes significantly less daunting, reducing the risk of introducing new bugs.

Remember, commenting isn't just about explaining what your code does, it is about illuminating the why behind it. By embracing effective commenting practices, we create code that is both functional and sustainable, benefiting not only our current project but also any future endeavors it may become a part of.

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Frequently Asked Questions

What are comments in C++?

Comments in C++ are lines of text that the compiler ignores, allowing you to add notes and explanations within your code.

How many types of comments are there in C++?

There are two types of comments in C++: single-line comments (//) and multi-line comments (/* */).

What is the purpose of comments in C++?

Comments in C++ are used to explain code, improve readability, and make it easier to understand and maintain, especially for yourself and other developers.

Why are comments used in C++?

Comments are used in C++ to:

• Explain complex logic or algorithms
• Clarify the purpose of variables or functions
• Temporarily disable code for testing
• Provide reminders or notes to yourself or other developers

Can comments be nested in C++?

No, comments cannot be nested within each other in C++.

How do you write comments in C++?

• Single-line comments: Begin with // and everything after that on the line is ignored.
• Multi-line comments: Begin with /* and end with */ and everything in between is ignored.

How do you comment in C++ shortcut?

Common shortcuts for commenting:

• Single-line comment: Ctrl + / (Windows), Cmd + / (Mac)
• Multi-line comment: Ctrl + Shift + / (Windows), Cmd + Shift + / (Mac)