Operations in doubly link list using header->next

#include<iostream.h>
#include<conio.h>
class dll
{
 struct dll_node
 {
 dll_node *prev,*next;
 int data;
 }*header,*first,*last,*nn;
 public:
 dll()
 {
 header=new dll_node;
 header->data=0;
 header->next=NULL;
 header->prev=NULL;
 last=NULL;
 }

 ~dll()
 void create(int);
 void display();
 void insertatbeg(int);
 void insertatend(int);
 dll_node* search(int);
 void insertkey(int,int);
 void insertbeforekey(int,int);
 void deleteatbeg();
};

void dll::create(int k)
{
dll_node *nn;
for(int i=1;i<=k;i++)
{
 nn=new dll_node;
 nn->data=i*10;
 nn->prev=NULL;
 nn->next=NULL;
 if(header->next==NULL)
 header->next=last=nn;
 else
 {
 nn->prev=last->next;
 last->next=nn;
 last=nn;
 }
}
display();
}
void dll::display()
{
dll_node *ptr;
cout<<endl;
for(ptr=header->next;ptr!=NULL;ptr=ptr->next)
cout<<ptr->data<<"->";
}
void dll::insertatbeg(int d)
{
nn=new dll_node;
nn->data=d;
 if(header->next==NULL)
 {
  nn->next=NULL;
  nn->prev=header;
  header->next=nn;
  last=nn;
  }
  else
  {

  nn->prev=header;
  nn->next=header->next;
  header->next=nn;
  nn->next->prev=nn;
  }
display();
}
void dll::insertatend(int d)
{
nn=new dll_node;
nn->data=d;
if(last==NULL)
{
header->next=last=nn;
}
else
{
nn->next=NULL;
nn->prev=last->next;
last->next=nn;
last=nn;
}
display();
cout<<"last="<<last->data;
}
dll_node* dll::search(int key)
{
dll_node *ptr;
for(ptr=header->next;ptr->next!=NULL && ptr->data!=key;ptr=ptr->next);
if(ptr!=NULL)
cout<<"Key "<<ptr->data<<" found";
else
cout<<"key "<<key<<" not found";
return ptr;
}

void dll::insertbeforekey(int key,int d)
{
dll_node *ptr,*nn;
nn=new dll_node;
nn->data=d;
ptr=search(key);
if(ptr!=NULL)
{
nn->next=ptr;
nn->prev=ptr->prev;
ptr->prev=nn;
nn->prev->next=nn;
}
else
cout<<"Insertion failed";
display();
}
void dll::insertafterkey(int key,int d)
{
dll_node *ptr;
nn=new dll_node;
nn->data=d;
ptr=search(key);
if(ptr!=NULL)
{

nn->next=ptr->next;
nn->prev=ptr;
ptr->next=nn;
nn->next->prev=nn;
}
else
cout<<"Insertion failed";
cout<<"last="<<last->data;
display();
}
void dll::deleteatbeg()
{
dll_node *ptr;
ptr=header->next;
if(header->next==NULL)
cout<<"Deletion is not possible";
else
header->next=ptr->next;
delete ptr;
cout<<"last="<<last->data;
display();
}
int main()
{
clrscr();
dll d;
cout<<"Create:";
d.create(7);
cout<<"\n\nInsert at beg:";
d.insertatbeg(58);
cout<<"\n\nInsert at end:";
d.insertatend(74);
cout<<"\n\nInsert before key:";
d.insertbeforekey(40,9);
cout<<"\n\nInsert after key:";
d.insertafterkey(40,5);
cout<<"\n\ndelete at beg:";
d.deleteatbeg();
getch();
return 0;
}

}