#include <iostream>
using namespace std;
void increment(int &m){ // alias int m = &a; address of m is the address of a
  m++;
  cout << " m is " << m << "\n";
}

int main(){ 
  int a = 0;
  cout << " a is " << a << "\n"; // output: a is 0
  increment(a);                  // output: m is 1 
  cout << " a is " << a << "\n"; // output: a is 1
  return 0; 
}