Answer 1

If you are talking about an arbitrary function's return then I have an example for you.

int func(double x); // This is a function prototype

....
int main() {
...
double pi = 3.14;
cout << func(pi);
...
}

// This is function definition
int func(double x) {
if (x > 0) return 0; // here, 3.14 > 0 then 0 is gonna return to caller and 0 prints out.
else return 2 + 2 // if you pass a negative number, then 2 + 2 = 4 will return and you'll see 4 in the console
}