#include <stdio.h>
#include <conio.h>
#define VAL 40
#ifdef VAL
#undef VAL
#endif
#define VAL 50
int main ()
{
clrscr();
printf( "\n Value = %d", VAL );
getch();
return 0;
}
输出
Value = 50
原文：https://www.cnblogs.com/sea-stream/p/10237143.html