What is prototyping in c plus plus?

A prototype in C++, as well as in C, is a declaration of a function and its parameters, including the types of the function and parameters. It does not actually create (define) the code for the function - it only identifies (declares) it to the compiler.

It is used to enforce type checking for functions and parameters, and it is used to declare the function for use in other code prior to the function actually being defined, such as in a different compilation unit or library. Headers, for instance, contain mostly prototypes.