The Waite Group's C++ Primer Plus, Third Edition

Recursion

And now for something completely different. A C++ function has the interesting characteristic that it can call itself. (Unlike C, however, C++ does not let main() call itself.) This ability is termed recursion. Recursion is an important tool in certain types of programming, such as artificial intelligence, but we'll just take a superficial look (artificial shallowness) at how it works.

If a recursive function calls itself, then the newly called function calls itself, and so on ad infinitum unless the code includes something to terminate the chain of calls. The usual method is to make the recursive call part of an if statement. For example, a type void recursive function called recurs() can have a form like this:

void recurs(argumentlist ...