Why the include doesn't work on mac command line tools?

Question

The code below works fine on Windows, but when I compile it on Mac's Xcode, I don't get any output.

#include <iostream>
#include <stack>

using namespace std;

int main(int argc, const char * argv[]) {
   stack<int> S;
   S.push(5);
   cout << S.top();
   return 0;
}