Programming Tutorials

Comments in C++

By: Stanley B. in C++ Tutorials on 2011-02-19  

There are two kinds of comments in C++: single-line and paired. A single-line comment starts with a double slash (//). Everything to the right of the slashes on the current line is a comment and ignored by the compiler.

The other delimiter, the comment pair (/* */), is inherited from the C language. Such comments begin with a /* and end with the next */. The compiler treats everything that falls between the /* and */ as part of the comment:

#include <iostream>
/* Simple main function: Read two numbers and write their sum */
int main()
// prompt user to enter two numbers
std::cout << "Enter two numbers:" << std::endl;
int v1, v2; // uninitialized
std::cin >> v1 >> v2; // read input
return 0;

A comment pair can be placed anywhere a tab, space, or newline is permitted. Comment pairs can span multiple lines of a program but are not required to do so. When a comment pair does span multiple lines, it is often a good idea to indicate visually that the inner lines are part of a multi-line comment. Our style is to begin each line in the comment with an asterisk, thus indicating that the entire range is part of a multi-line comment.

Programs typically contain a mixture of both comment forms. Comment pairs generally are used for multi-line explanations, whereas double slash comments tend to be used for half-line and single-line remarks.

Too many comments intermixed with the program code can obscure the code. It is usually best to place a comment block above the code it explains.

Comments should be kept up to date as the code itself changes. Programmers expect comments to remain accurate and so believe them, even when other forms of system documentation are known to be out of date. An incorrect comment is worse than no comment at all because it may mislead a subsequent reader.

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