#include <iostream>
using namespace std;

void swap(int *a, int *b)
{
  cout << "before swap a is " << a << ", b is " << b << endl;
  int t = *a;
  *a = *b;
  *b = t;
  cout << "before swap a is " << a << ", b is " << b << endl;
}

int main()
{
  double a = 9.9;
  double &b = a;  // 相当于 b 是 a 的别名
  b = 3.14;
  cout << "a is " << a << endl;

  int x = 1, y = 2;
  swap(&x, &y);
  cout << "swap x is " << x << ", y is " << y << endl;

  return 0;
}