交换两个变量以及不使用第三个变量

int n1 = 10,n2 = 20;

tmp = n1;

n1 = n2;

n2 = tmp;

 

n1 = n1+n2;

n2 = n1-n2;

n1 = n1-n2;

 

n2 = n1+(n1+n2) ) * 0;