Uses of function prototype in C or C++ programming language

The real use of using function prototype in C or C++ programming language is for to Informing the compiler

If a function is not earlier declared and its name takes place in an expression followed by a left parenthesis, it is implicitly affirmed as a function that returns an int and nothing is assumed about its arguments. In this case the compiler will not be able to perform compile-time checking of argument types and arity when the function is applied to various arguments. This can potentially root problems.