Comments in C++ are used to add annotations or explanations to the code. They are ignored by the compiler and do not affect the execution of the program. There are two types of comments in C++: single-line comments and multi-line comments.

Single line comments start with `//` and continue to the end of the line. For example:

``````1// This is a single line comment
2int x = 10;``````

In the above code, the line `// This is a single line comment` is a single line comment and is ignored by the compiler.

Multi-line comments start with `/*` and end with `*/`. For example:

``````1/* This is a
2   multi-line comment */
3int x = 10;``````

In the above code, the text between `/*` and `*/` is a multi-line comment and is ignored by the compiler.

### Examples

Here are some examples of comments in C++:

``````1// This program calculates the area of a circle
2#include <iostream>
3#include <cmath>
4
5int main()
6{
7    double r;
8    const double pi = 3.14159265;
9
11    cout << "Enter the radius: ";
12    cin >> r;
13
14    // Calculate the area
15    double area = pi * pow(r, 2);
16
17    // Output the result
18    cout << "The area is: " << area << endl;
19
20    return 0;
21}``````
``````1/* This program calculates the factorial of a number
2   using a loop */
3#include <iostream>
4
5int main()
6{
7    int n;
8    int result = 1;
9
10    // Input a positive integer
11    cout << "Enter a positive integer: ";
12    cin >> n;
13
14    // Calculate the factorial
15    for (int i = 1; i <= n; i++)
16    {
17        result *= i;
18    }
19
20    // Output the result
21    cout << "The factorial of " << n << " is " << result << endl;
22
23    return 0;
24}``````