交换变量值的5种方法

 1 #include <stdio.h>
 2 
 3 #define swap_macro_0(a, b) 
 4     do { 
 5             typeof(a) c; 
 6             c = a; 
 7             a = b; 
 8             b = c; 
 9     } while(0)
10 
11 #define swap_macro_1(a, b) 
12     do { 
13             a = a + b; 
14             b = a - b; 
15             a = a - b; 
16     }while(0)
17 
18 #define swap_macro_2(a, b) 
19     do { 
20             a = a ^ b; 
21             b = a ^ b; 
22             a = a ^ b; 
23     }while(0)
24 
25 #define swap_macro_3(a, b) 
26     do { 
27            a = a * b; 
28            b = a / b; 
29            a = a / b; 
30     }while(0);
31     
32 #define swap_macro_4(a, b) 
33     do { 
34             a = a + b - (b = a); 
35     }while(0);
36     
37 int main()
38 {
39     int type, a, b;
40     
41     scanf("%d, %d, %d", &type, &a, &b);
42     printf("before a = %d, b = %d
", a, b);
43     switch(type)
44     {
45         case 0:
46             {
47                 swap_macro_0(a, b);
48                 break;
49             }
50         case 1:
51             {
52                 swap_macro_1(a, b);
53                 break;
54             }
55         case 2:
56             {
57                 swap_macro_2(a, b);
58                 break;
59             }
60         case 3:
61             {
62                 swap_macro_3(a, b);   
63                 break;      
64             }
65         case 4:
66             {
67                 swap_macro_4(a, b);   
68                 break; 
69             }
70         default:
71             {
72                 printf("unknown swap type!
");
73                 return 0;
74             }
75     }
76     printf("after a = %d, b = %d
", a, b);
77     return 0;
78 }