#include<iostream>
using namespace std;
//利用引用进行交换
void swap(int &a,int &b) {
int t;
t = a;
a = b;
b = t;
cout << a << endl;
cout << b << endl;
}
int main() {
int a = 10;
int b = 20;
cout << a << endl;
cout << b << endl;
swap(a,b);
return 0;
}