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 }