/* 两数交换.cpp */
#include <iostream>
using namespace std;
void swap(int &a, int &b);
int main(int argc, char const *argv[]) {
  int x1(5);
  int x2(7);
  swap(x1, x2);
  cout << x1 << " " << x2 << endl;
  
  return 0;
}

void swap(int &a, int &b) {
  int t;
  t = a;
  a = b;
  b = t;
}