Why prototype is required even without any class declaration?

Question

If I just do it: Ex1:

#include 

int main()
{
    //try to call doSomething function
    doSomething();
}

void doSomething(         


        

Answer 1

You can't call a function without the compiler having seen either the definition or a declaration, first -- simple as that. A prototype or the actual definition must appear before a call.