交换两个数，不引入第三个变量

#include<stdio.h>

int main()
{
    int a = 1;
    int b = 2;
    printf("Initial:\n");
    printf("a = %d\n", a);
    printf("b = %d\n", b);
    a = a + b;
    b = a - b;
    a = a - b;
    printf("Swap:\n");
    printf("a = %d\n", a);
    printf("b = %d\n", b);
    return 0;
}

     有人可能会觉得此算法会溢出，你可以用a = 0x7fffffff, b = 0x7ffffffe代替上面的赋值语句，来代替，得到的结果是一样的，如果还不放心，下面介绍另一种算法，通过位运算来实现变量的交换。

#include<stdio.h>
 
 int main()
 {
     int a = 0x7fffffff;
     int b = 0x7ffffffe;
     printf("Initial:\n");
     printf("a = %d\n", a);
     printf("b = %d\n", b);
     a ^= b;
     b ^= a;
     a ^= b;;
     printf("Swap:\n");
     printf("a = %d\n", a);
     printf("b = %d\n", b);
     return 0;
 }