Create an instance of a class in the class itself [duplicate]

Question

I am new to C++ and have a question:

Compare following code:

class Node { 
public:
    int data;
    Node* x;
};

and

class Node { 
public:
    int data;
    Node x;
};

I know the second part of code can't pass compile. But I want to know the reason.

Is it related to memory allocation or just syntax regulation?

I would be appreciate if someone can solve my question.

Answer 1

If you could, then a Node would contain a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node, which contains a Node... and so on until the universe is full of Nodes and implodes.