Comments are text blocks that the compiler will ignore. Comments provide additional information that can not be easily expressed in code. They are a good way to leave notes about why the code is written as it is, since even a single programmer tends to forget things. Comments are indispensable in large programmer teams.

There are two ways to declare a comment block in C++:

  • Single-line comment. The compiler always ignores everything after // till the end of a line.
  • Multi-line comment. The compiler always ignores everything between /* and */. Be sure that the comment itself does not contain */, because this would cause the compiler to end the comment prematurely and probably emit an error, since the rest of the comment is usually not proper C++.

The following example demonstrates the usage of comments in the "Hello world!" program:

/* Hello world example
   This comment spans several lines
#include <iostream>
int main() /* This comment spans part of a line */
    std::cout << "Hello World!\n"; // till the end of the line
    return 0;


Hello World!