text: #include <iostream>
  
  using namespace std;
  
  int add(int x, int y) { return x + y; }
  
  int subtract(int x, int y) { return x - y; }
  
  int common_operator(int x, int y, int (*function)(int, int)) {
    return (*function)(x, y);
  }
  
  int main() {
    cout << common_operator(1, 2, add) << endl;
    cout << common_operator(1, 2, subtract) << endl;
  }