void swap(int &a, int &b)
{
//方法一：
int tmp = 0;
tmp = b;
b = a;
a = tmp;
//方法二：
//a = a+b;
//b = a-b;
//a = a -b;
//方法三：
//a ^= b ^= a ^= b;
//方法四：
//a = a+b-(b=a);
}

int main(void)
{
int a = 3;
int b = 4;

printf("before swap: a = %d, b = %d/n", a, b);
swap(a, b);
printf("after swap: a = %d, b = %d/n", a, b);

return 0;
}