Swap函数的N种写法

异或运算中有这样的一个性质：a == a^b^b，
计算过程是：
a = a ^ b
b = b ^ (a^b)
a = (a^b) ^ (b^a^b)

void swap(int* a, int* b)
{    
	//(1)用异或运算
	  
	*a ^= *b;     
	*b ^= *a;     
	*a ^= *b;
	
	*a ^= *b ^= *a ^= *b;
	
	*a ^= (*b ^= (*a ^= *b));
	
	//(2)用加减运算
	   
	*a = *a + *b;
	*b = *a - *b;
	*a = *a - *b;
	
	//2、引入中间变量
	
	int t = *a;
	*a = *b;
	*b = t;
}