#if #elif Considerations when using #define TypeDef

Let's say the following code is required to be compatible with three versions

This will not complete the task.

No matter

typedef enum{first,second,third,}; #define NUM  third#if (num = = first) #define  VAR  1#elif (num = = SECOND) # Define  var  2#elif (num = = third) #define  var  3#endifint main (void) {#if (num = = first) printf ("VAL =%d\n" , Var), #elif (num = = SECOND) printf ("val =%d\n", var), #elif (num = = third) printf ("val =%d\n", var); #endif}

#define NUM First or

#define NUM Second or

#define NUM Third

The results are all the same

But then we can do the job.

#define FIRST    1#define SECOND   2#define third    3#define num  third#if (num = = first) #define  VAR  1#elif (num = SECOND) #define  var  2#elif (num = = third) #define  var  3#endifint main (void) {#if (num = = First) printf ("val =%d\n", var), #elif (num = = SECOND) printf ("val =%d\n", var), #elif (num = = third) printf ("val =%d\n", var); #endif}

#define NUM First or

#define NUM Second or

#define NUM Third

Can get the results you want.

Why?????

#if #elif Considerations when using #define TypeDef