Self referring structure declaration

Question

The follwing declaration is valid.

struct node
{
    int a;
    struct node *next;
};

However, when we define the following, it gives error.

Answer 1

You can't have structure that contains itself as a member:

struct node
{
    int a;
    struct node next;
};

Think about this question: if it is possible, what is the size of such structure? struct node contains struct node next as a member, then the member next would contain a member of type struct node as well, and so on and on and on... The size would be infinite.