解法1（引第三变量）
#include<stdio.h>
int main()
{
int a = 3;
int b = 5;
int tmp = 0;
printf("before：a=%d b=%d\n",a,b);
tmp = a;
a = b;
b = tmp;
printf("after：a=%d b=%d\n",a,b);
return 0;
} //效率高解法2（加减法）
#include<stdio.h>
int main()
{
int a = 3;
int b = 5;
printf("before：a=%d b=%d\n",a,b);
a = a+b;
b = a-b;
a = a-b;
printf("after：a=%d b=%d\n",a,b);
return 0;
} //此代码可能会溢出，少用解法3（异或法）
#include<stdio.h>
int main()
{
int a = 3;
int b = 5;
printf("before：a=%d b=%d\n",a,b);
a = a^b;
b = a^b;
a = a^b;
printf("after：a=%d b=%d\n",a,b);
return 0;
}
