C Programming - Declarations and Initializations - Discussion

Anyone please explain the right answer.

According to me the, best possible reason can be:

Structure is a user-defined data type, so when we declare any variable using that data type, that var get the size of that datatype.

Now here in structure 2, we have declared the strct type variable, before the complete declaration of struct, hence it gives the error.

But in structure 3, we can define a pointer of the same type, as it is fixed that any pointer will always take a space of 4 bytes.

B. is incorrect because there is no declaration of struct aa;

But in c there is pointer *aa so it can declare it self as a garbage value.

Thank you @Jarvis.

Shall I declare struct aa var; outside the structure? Can Anyone explain, please?

You can not put a whole struct inside of itself because it would be infinitely recursive.

But you can put the address of another instance of a struct inside of a struct; which is what a pointer is. An address the size of SomeStruct* is always the same, so the compiler knows how much memory to make for one instance of the struct.

Please explain briefly I can't understand.

Because pointer and structure are same data types (user defined).

I think C is the correct answer.

I am not understanding this. Please, anyone explain this.