交换两个数字，不借助于第三个变量的三种简单的方法。

 1 #include <stdio.h>

 2 int main()

 3 {

 4     int a = 10,b=20;

 5 //  solution 1: a = a+b; b = a-b; a = a-b;

 6     printf("*********************************************\n");

 7     printf("Change two number without another number!!!!\n");

 8     printf("*********************************************\n");

 9     printf("Solution 1:\n");

10     printf("a:%d b:%d\n",a,b);

11     a = a + b;

12     b = a - b;

13     a = a - b;

14     printf("a:%d b:%d\n",a,b);    

15     printf("*********************************************\n");

16     printf("Solution 2:\n");

17 //  solution 2:

18     a = 10;

19     b = 20;

20     printf("a:%d b:%d\n",a,b);

21     a = a*b;

22     b = a/b;

23     a = a/b;

24     printf("a:%d b:%d\n",a,b);

25     

26     printf("*********************************************\n");

27     printf("Solution 3:\n");

28 //  solution 3:a^=b^=a^=b; 

29     a = 10;

30     b = 20;

31     printf("a:%d b:%d\n",a,b);

32     a = a^b;//put the information into a

33     b = a^b;//make b equal to the orginal a

34     a = a^b;//make a equal to the orginal b

35     printf("c:%d d:%d\n",a,b);

36 

37     return 0;

38 }