Explain why the output is 12 instead of 9

Question

#include <iostream>
using namespace std;
#define sq(x) (x)*(x)
int main() {
int a=3;
cout<<sq(a++);
return 0;
}

Answer 1

You increment a by one with the '++' term after the first operation, so it is 3 times 4 = 12. Delete ++ to calculate the square of 3.