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Comments

Learn to write single-line (//) and multi-line (/* */) comments in C++.

Comments

Comments are notes for the programmer; the compiler ignores them. C++ has two kinds of comments:

  • Single-line comment: starts with // and runs to the end of the line
  • Multi-line comment: starts with /* and ends with */, spanning several lines

Comments explain code, temporarily disable lines or mark sections. But do not write comments instead of working code; code should explain itself.

Using comments

Comments make code readable. They are especially useful for:

  • Explaining complex logic: // b cannot be zero for division
  • Adding section headers: // --- Calculation section ---
  • Temporarily hiding a line (commenting it out)

Example:

// User score
int score = 90;
/* In this section
   the score is computed */

With clear names you need fewer comments; comments should explain why, not what.

Practice Add comments and output

Add a // comment, a /* */ comment to the program, and print the message Program ready with std::cout.

Starter code

main.cpp
#include <iostream>

int main() {
    return 0;
}

Sample solution

main.cpp
#include <iostream>

int main() {
    // Information
    /* This program is ready */
    std::cout << "Program ready" << std::endl;
    return 0;
}

Expected output

Program ready

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 How does a multi-line comment start?

  • With /* Correct answer
  • With ///
  • With //
  • With <!--

Explanation: A multi-line comment starts with /* and ends with */.

2 Match the comment types

Term Meaning
// Single-line comment
/* */ Multi-line comment
compiler Ignores comments
section header Added via comment

3 Single-line comment

Question 
// Score ____ 90
Answer 
// Score value: 90

Explanation: 'value:' is an explanatory note inside a comment.

All lessons in Beginner

1 C++ basics

  1. What is C++?
  2. Your first program
  3. std::cout
  4. std::cin
  5. Comments
  6. Summary - C++ basics

2 Variables

  1. Declaring variables
  2. auto
  3. const
  4. constexpr
  5. Type conversion
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and char
  4. std::string
  5. sizeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 Strings

  1. std::string basics
  2. String concatenation
  3. String length
  4. Substring
  5. String search
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range-based for
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. C-style arrays
  2. Array access
  3. std::array
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 std::vector

  1. Declaring vectors
  2. push_back
  3. size and at
  4. Vector access
  5. Vector loop
  6. Summary - std::vector

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function overloading
  5. Default parameters
  6. Summary - Functions

13 References

  1. What is a reference?
  2. Declaring references
  3. Reference parameters
  4. const references
  5. Dangling references
  6. Summary - References

14 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. nullptr
  5. Pointer arithmetic
  6. Summary - Pointer basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. String streams
  2. stoi and stod
  3. to_string
  4. String comparison
  5. String modification
  6. Summary - Advanced strings

17 Structs

  1. Defining structs
  2. Using structs
  3. Struct and function
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Exception basics

  1. try/catch
  2. throw
  3. std::exception
  4. Custom exceptions
  5. catch all
  6. Summary - Exceptions

19 Namespaces

  1. Defining namespaces
  2. using
  3. std namespace
  4. Nested namespaces
  5. Namespace alias
  6. Summary - Namespaces

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together