C++ Tutorial/Operator Overloading/overload address of operator

#include <iostream>
using namespace std;
class Point {
  int a[3];
public:
  Point(int i, int j, int k) {
    a[0] = i;
    a[1] = j;
    a[2] = k;
  }
  int &operator[](int i) { return a[i]; }
};
int main()
{
  Point ob(1, 2, 3);
  cout << ob[1]; // displays 2
  cout << " ";
  ob[1] = 25; // [] on left of =
  cout << ob[1]; // now displays 25
  return 0;
}