what do you mean by function protoypes?

function prototype is a declaration of a function that omits the function body but does specify the function's name, arity, argument types and return type. While a function definition specifies what a function does, a function prototype can be thought of as specifying its interface. In a prototype, argument names are optional, however, the type is necessary along with all modifiers (i.e. If it is a pointer or a const argument). Example: int fac(int n);