namespace CppLists
{
    struct List;
    struct Node
    {
        Node* next;
        int data;
        Node* prev;
    };

    struct List
    {
        List();
        Node* first;
        Node* last;
        int size;
    };
}
____________________________________

#include "CppLists.h"
#define NULL 0

CppLists::List::List()
{
        size = 0;
        first = NULL;
        last = NULL;
}