#include "stdafx.h"
#include <iostream>

using namespace std;
struct Double_node{
int val;
Double_node * next;
Double_node * prev;

};


class Double_list{
private:
    Double_node *tail;
public:
    Double_list();
    Double_list(int);
    ~Double_list();
    bool empty();
    void push_front(int);
    void pop_front();
    void push_back(int);
    void pop_back();
    void clear();
    int& front();
    int& back();
    int size();
    void print();
};

Double_list::Double_list()
{
    tail=0;

}
Double_list::Double_list(int a)
{
            Double_node *p = new Double_node;
            p->val=0;
            p->prev=tail;
            p->next=tail;
}

bool Double_list::empty()
{
    if(tail->next==tail->prev)
        return true;
        else return false;
}
void Double_list::push_front(int a)
{
    Double_node *p= new Double_node;
    p->val = a;
    p->prev = tail;
    p->next = tail->next;
}
void Double_list::pop_front()
{
    if(tail->next!=tail->prev)
    {
        Double_node *node = tail->next->next;
        delete tail->next;
        tail->next = node;
    }
}
void Double_list::clear()
{
    while(tail->next!= tail->prev)
    {
        Double_node *node = tail->next->next;
        delete tail->next;
        tail->next = node;
    }

}
int& Double_list::front()
{
    return tail->next->val;
}
int Double_list::size()
{
    Double_node *p=tail->next;
    Double_node *t=tail;
    int k=0;
    while(p->next != t)
    {
        p=p->next;
        k++;
    }
    return k;
}
void Double_list::print()
{
    Double_node *p=tail->next;
    while(p != tail)
    {
        cout<<p->val<<" ";
        Double_node *node = p->next;
        p = node;
    }
    cout<<"\n";
}
Double_list::~Double_list()
{

   while(tail->prev != tail->next )
    {
        Double_node *node = tail->next->next;
        delete tail->next;
        tail->next = node;
    }

}


int main()
{
    Double_list();
    return 0;
}