各种宏，看的我头晕眼花，求讲解 - C语言论坛

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各种宏，看的我头晕眼花，求讲解

今天看一个程序，里面各种的宏，除了头几个其他的我是真不认识，上网上找，总感觉答非所问，求教

程序代码：

#include"stdio.h"
#define MAX
#define MAXIMUM(x,y) (x>y)?x:y
#define MINIMUM(x,y) (x>y)?y:x
void main()
{
    int a=10,b=20;
    #ifdef MAX
    printf("\40:The larger one is %d\n",MAXIMUM(a,b));
    #else
    printf("\40:The lower one is %d\n",MINIMUM(a,b));
    #endif
    #ifndef MIN
    printf("\40:The lower one is %d\n",MINIMUM(a,b));
    #else
    printf("\40:The larger one is %d\n",MAXIMUM(a,b));
    #endif
    #undef MAX
    #ifdef MAX
    printf("\40:The larger one is %d\n",MAXIMUM(a,b));
    #else
    printf("\40:The lower one is %d\n",MINIMUM(a,b));
    #endif
    #define MIN
    #ifndef MIN
    printf("\40:The lower one is %d\n",MINIMUM(a,b));
    #else
    printf("\40:The larger one is %d\n",MAXIMUM(a,b));
    #endif
    return 0;
}

有明白的帮帮忙，主函数里带井号我是一个不认识，求帮助