#include <iostream>
using namespace std;
void xchg(____________________) { // 在此处填入代码
    int t = *x;
    *x = *y;
    *y = t;
}
int main() {
    int a = 10, b = 20;
    xchg(&a, &b);
    cout << a << " " << b << endl;
    return 0;
}