Just for the sake of clarity, let's define what a function prototype is. I've learned that: is a function prototype, it tells the compiler what a function will return and what arguments must be passed on a call to it. It is used in header files, class method declarations and for forward declarations. while:
would be called the function declaration or implementation (well, it contains a function prototype).
int myfn(int x)
// do something in here
I might be wrong but this is the way i have learned, so a header file will most of the times (there will always be exceptions) include function prototypes, but only in some cases will it contain function implementations.
Again, this is how i've learned but i'm no c++ master by any means.
P.S - If what i've learned is right then Daved is correct and the question is in itself wrong.