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

Because the compiler hasn't seen doSomething before it's used.

Either you must prototype it, or define it first, so that the compiler knows how to analyze the usage of it.