void reference_operator_example()
{
  int x;
  std::string y = "hello world!";


  // these three lines use & as the reference operator.
  std::cout << "the address of x is: " << &x << std::endl;
  std::cout << "the address of y is: " << &y << std::endl;

  // this assignment changed the value of x but does not change
  // its address
  x = 7;
  std::cout << "the address of x is still " << &x << std::endl;
}