不用第三方参数，交换两个参数的值

#include <iostream>
using namespace std;

void Swap1(int &a, int &b) { a = a + b - (b = a); }

int main(){
	int a = 4, b = 5;
	cout << "before swap: ";
	cout << "a = " << a << ", b = " << b << endl;
	Swap1(a, b);
	cout << "after swap: ";
	cout << "a = " << a << ", b = " << b << endl;
	return 0;
}