Реализовать указанные функции-члены для пользовательского класса "Кольцевой двусвязный список"

#include <iostream>
using namespace std; 
struct Double_node
{
    Double_node *next;
    Double_node *prev;
    int val;
    Double_node() {}
    Double_node(int x) { val = x; };
    Double_node(int a, Double_node* b, Double_node* c) { val = a; next = b; prev = c; };
};
class Double_list
{
private:
    Double_node *tail;
    int sz;
public:
    Double_list() { tail = new Double_node; sz = 0; };
 
    Double_list(int x) { tail = new Double_node(x);  tail->next = tail; tail->prev = tail; sz = 1; };
 
    ~Double_list() { while (!tail) { Double_node* tmp; tmp = tail->next; delete tail->next; tmp = tmp->next; } delete tail->prev; sz = 0; }
 
    bool is_empty() { return sz == 0; };
 
    void add_front(int x) { tail->prev = new Double_node(x, tail->prev, tail); sz++; };
 
    void add_rear(int x) { tail->next = new Double_node(x, tail->next, tail); sz++; };
 
    void insert_after(int n, int x) { Double_node* tmp = tail->prev; for (int i = 0; i < n - 2; i++) tmp = tmp->next; Double_node* mem1 = tmp->next; Double_node* mem2 = tmp; tmp->next = new Double_node(x, mem1, mem2); sz++; }
 
    int remove(int x) { Double_node* tmp = tail->prev; for (tmp; tmp != tail; tmp = tmp->next) { if (tmp->val == x) { int mem = tmp->val; tmp->prev->next = tmp->next; delete tmp; sz--; return mem; } } };
 
    int remove_front() { int memory = tail->prev->val; Double_node* mem = tail->prev; mem->prev = tail; tail = mem->next; delete mem; sz--; return memory;  }
 
    int remove_rear() { int memory = tail->next->val; Double_node* mem = tail->next; tail->next = mem->next; mem->next->prev = tail; delete mem; sz--; return memory; }
 
    bool find(int x) { Double_node* tmp = tail->prev; for (tmp;tmp!=tail; tmp = tmp->next) { if (tmp->val == x) return true; }return false; };
 
    int get_nth(int n) { Double_node* tmp = tail->prev; for (int i = 0; i < n-2; i++) tmp = tmp->next; return tmp->val; };
 
    int size() { return sz; }
 
    };

    list.insert(list.rbegin()+1, 28);
        list.print();

void remove_iter(iterator it)
    {
        Double_node* mem = it.node;
        Double_node* mem_next = (it++).node;
        Double_node* mem_prev = (it--).node;
        mem_prev->next = mem_next;
        mem_next->prev = mem_next;
        delete it.node;
        sz--;
    }

void remove_iter(iterator it)
    {
        Double_node* mem = it.node;
        Double_node* mem_next = (++it).node;
        --it;
        Double_node* mem_prev = (--it).node;
        ++it;
        mem_prev->next = mem_next;
        mem_next->prev = mem_prev;
        delete it.node;
        sz--;
    }

iterator& operator++(int)
        {
            node = node->next;  
            return *this;
        }
iterator operator++()   
        {
            iterator it(node);  
            node = node->next;
            return it;
        }

    list.insert(list.rbegin()+1, 28);
        list.print();

    list.insert(++list.rbegin(), 28);
        list.print();

list.insert(++list.rbegin(), 28);