What will be the result of #define a 1 or undefined variable # if a==1 in c language

in c language,

#define a 1  
#if a==1  
#define b  
#if b==1

What will be the result?

in conclusion

define	#ifdef WAS	#if defined(VAR)	#if VAR ==1	#if VAR ==0
#define VAR 1	true	true	true	false
#define WAS 0	true	true	false	true
#define WHERE	true	true	ERROR (compilation failed)	ERROR
#undefine WAS	false	false	false	true
None	false	false	false	true

1. #undefine VAR is equivalent to not defining VAR
2. #ifdef VAR is equivalent to #if defined(VAR)
3. Undefined VAR is equivalent to 0
4. If you want multiple conditions you can
   #if defined(VAR_A) || VAR_B==1
5. If you want multiple conditions you can
   #if defined(VAR_A) && VAR_B==1