c++ iki yönlü linked list uygulaması

#include <iostream>
using namespace std;
class veri{
    public:
    int a;
    veri* next,*back;
};
class liste{
    int sayac;
    veri* head,*current;
    public:
        liste(){
            sayac=0;
        }
        **** baslat(int y){
            head=new veri;
            head->a=y;
            current=new veri;
            head->next=current;
            current->back=head;
        }
        **** ekle(int y){
            current->a=y;
            current->next=new veri;
            current->next->back=current;
            current=current->next;
            sayac=sayac+1;
        }
        **** sil(int y){
            veri* plm=head,*plm2=head;
            if(y==head->a){
                head=head->next;
                delete plm2;
                sayac--;
                sil(y);
            }
            if(y==current->a){
                for(int i=0;i<=sayac-1;i++){
                    plm=plm->next;
                    plm2=plm2->next;
                }
                plm->next=current->next;
                plm2->next=current->next;
                plm->back=current->back;
                plm2->back=current->back;
                delete current;
                sayac--;
                sil(y);
            }
            for(int i=0;i<=sayac;i++){
                if(y==plm->a){
                    plm2->back=plm->back;
                    plm2->next=plm->next;
                    delete plm;
                    sayac--;
                    sil(y);
                }
                plm=plm->next;
                
                plm2=plm2->next;
            }
        }
        
        int len(){
            return sayac;
        }
        int uzunluk(){
            return sayac;
        }
        veri* getItemAt(int y){
            veri* plm=head;
            for(int i=0;i<y;i++){
                if(plm->next){
                    plm=plm->next;
                }
            }
            return plm;
        }
        **** yazdir(){
            veri* plm=head;
            for(int i=0;i<=len();i++){
                cout<<plm->a<<"  "<<plm->next<<"  "<<plm->back<<endl;
                plm=plm->next;
            }
        }
};
int main(){
    liste plm;
    plm.baslat(1);
    for(int i=2;i<=4;i++){
        plm.ekle(i);
    }
    plm.sil(1);
    plm.yazdir();
    char y;cin>>y;
}