定义临时变量

定义一个中间变量用来交换两个数。就如同要把两杯水交换，可以借助第三个杯子，进行交换。代码如下：

#include<stdio.h>
#include<stdlib.h>
//最简单的定义中间变量
int main()
{
	int a = 7;
	int b = 8;
	int tem;
	printf("交换前：a=7,b=8\n");
	if (a != b)
	{
		tem = a;
		a = b;
		b = tem;
	}
	printf("交换后：a=%d,b=%d\n", a, b);
	system("pause");
	return 0;
}

//将其封装成函数
#include<stdio.h>
#include<stdlib.h>
void Swap(int *p1,int *p2)
{
	int tmp = 0;
	tmp = *p1;
	*p1 = *p2;
	*p2= tmp;
}
int main()
{
	int a = 3;
	int b = 6;
	printf("%d %d\n", a, b);
	Swap(&a, &b);//传址调用
	printf("%d %d", a, b);
	system("pause");
	return 0;
}

无临时变量

采用两数先相加再相减的方式，该方法的问题在于可能存在两数相加会溢出的问题

#include<stdio.h>
#include<stdlib.h>
int main()
{
	int a = 10;
	int b = 20;
	printf("a=%d b=%d\n", a, b);
	a = a + b;
	b = a - b;
	a = a - b;
	printf("a=%d b=%d\n", a, b);
	system("pause");
	return 0;
}

异或的方式

#include<stdio.h>
#include<stdlib.h>
int main()
{
	int a = 9;//1001
	int b = 5;//0101
	printf("交换前：a=%d b=%d\n", a, b);
	a = a^b; //a=1001^0101=1100
	b = a^b;//b=1100^0101=1001=9
	a = b^a;//a=1001^1100=0101=5
	printf("交换后：a=%d b=%d\n", a, b);
	system("pause");
	return 0;
}