C language: comprehensive application of if, def and ifndef

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

Running results ：

 The bigger number is ：20
 The bigger number is ：20
 The smaller number is ：10
 The bigger number is ：20