#if #ifdef和#ifndef的综合应用。

 1 #include<stdio.h>
 2 
 3 #define MAX
 4 
 5 #define MAXIMUM(x,y) x>y?x:y
 6 #define MINIMUM(x,y) x<y?x:y
 7 
 8 int main()
 9 {
10     int a=10,b=20;
11 
12 #ifdef MAX
13     printf("\40:The larger one is %d\n",MAXIMUM(a,b));
14 #else
15     printf("\40:The lower one is %d\n",MINIMUM(a,b));
16 #endif
17 
18 
19 #ifndef MIN
20     printf("\40:The lower is %d\n",MINIMUM(a,b));
21 #else
22     printf("\40:The larger one is %d\n",MAXIMUM(a,b));
23 #endif
24 
25 #undef MAX
26 #ifdef MAX
27     printf("\40:The larger one is %d\n",MAXIMUM(a,b));
28 #else
29     printf("\40:The lower one is %d\n",MINIMUM(a,b));
30 #endif
31 
32 
33 #define MIN
34 #ifndef MIN
35     printf("\40:The lower one is %d\n",MINIMUM(a,b));
36 #else
37     printf("\40:The larger one is %d\n",MAXIMUM(a,b));
38 #endif
39     return 0;
40 
41 }