Why is NULL undeclared?

Question

I have a problem with this struct contructor when I try to compile this code:

typedef struct Node
{
    Node( int data ) //
    {
        this->data = dat         


        

Answer 1

Don't use NULL, C++ allows you to use the unadorned 0 instead:

previous = 0;
next = 0;

And, as at C++11, you generally shouldn't be using either NULL or 0 since it provides you with nullptr of type std::nullptr_t, which is better suited to the task.