C语言#define定义宏的使用详解

#define SUM(x,y) ((x)+(y))
int main()
{
    int a = 10;
    int b = 20;
    int ret = SUM(a, b);
    printf("%d\n", ret);
    return 0;
}

#define NUM(x,y) x+y
int main()
{
    int a = 2;
    int b = 3;
    printf("%d\n", NUM(a, b) * NUM(a, b));
    //结果：11
    return 0;
}

#define MAX(a, b) ( (a) > (b) ? (a) : (b) )
int main()
{
    int x = 5;
    int y = 8;
    int z = MAX(x++, y++);
    printf("x=%d y=%d z=%d\n", x, y, z);//输出的结果是什么
    return 0;
}
//( (x++) > (y++) ? (x++):(y++) )
//输出结果：x=6,y=10,z=9

int main()
{
#if 4>2
    printf("hello world!\n");
#endif
    return 0;
}
//输出hello world

int main()
{
#if 1>2
    printf("xixi\n");
#elif 4>3
    printf("haha\n");
#else 
    printf("heihei\n");
#endif
    return 0;
}
//输出结果：haha

  ```c
  
  #define DEF    
  int main()
  {
  #if defined(DEF)
      printf("haha\n");
  #endif
  
  #ifdef MAX
      printf("heihei\n");
  #endif
      return 0;
  }
  //输出结果：haha
  ```

#define DEF
int main()
{
#undef DEF//删除DEF宏定义了
#ifdef DEF
    printf("hehe\n");
#endif
    return 0;
}