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

#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

55555555555555555555555555求帮助

     #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

解释这个就差不多了，意思就是定义了MAX就编译printf("\40:The larger one is %d\n",MAXIMUM(a,b));否则编译 printf("\40:The lower one is %d\n",MINIMUM(a,b));

属于条件编译，不全是宏声明。#ifdef这个其实是“if define”的缩写，就是如果宏定义了max，

就执行语句（1），否则执行语句（2），即根据条件来编译，这里的条件就是宏声明了max.

#ifdef MAX
    printf("\40:The larger one is %d\n",MAXIMUM(a,b));（1）
    #else
    printf("\40:The lower one is %d\n",MINIMUM(a,b));（2）

 #undef 则是用来结束宏声明MAX，在这个语句之后的MAX如果没有重新定义，那它就没有意义了。属于未声明的变量了