DLL implemented

#include "dll.h"
Node::Node(int data, Node* prev, Node* next){
  _data = data;
  _prev = prev;
  _next = next;
}

DLL::DLL(){
  _head = _tail = _curr = 0;
}
DLL::~DLL(){
  while(del());
}
void DLL::copy(DLL& D){
  int curpos;
  for(curpos=0;D.goPrev();curpos++); // findout where is current
  if(!D.isEmpty()){
    do{
      this->append(D.visit());
    }while(D.goNext());
  }
  for(D.goHead(), this->goHead();curpos;D.goNext(), this->goNext(),curpos--);
}
DLL::DLL(DLL& D){
  _head = _tail = _curr = 0;
  copy(D);
}
DLL& DLL::operator=(DLL& D){
  while(del());
  copy(D);
  return *this;
}

void DLL::append(int data){
  Node* newnode = new Node(data);
  if(_tail){  // ! empty
    _tail->_next = newnode;
    newnode->_prev = _tail;
    _tail = _curr = newnode;
  }
  else{
    _tail = _curr = _head = newnode;
  }

}
int DLL::remove(){
  int data = visit();
  del();
  return data;
}
bool DLL::del(){
  bool ok = false;
  if(_curr){
    ok = true;
    Node* todel = _curr;
    if(_curr->_next){
      _curr->_next->_prev = _curr->_prev;
    }
    else{
      _tail = _tail->_prev;
    }
    if(_curr->_prev){
      _curr->_prev->_next = _curr->_next;
    }
    else{
      _head = _head->_next;
    }
    _curr = _curr->_next;
    delete todel;
  }
  return ok;
}
void DLL::insert(int data){
  if(_head == _curr){
    _head = new Node(data, (Node*)0, _head);
    _curr->_prev = _head;
  }
  else {
    _curr->_prev = new Node(data, _curr->_prev, _curr);
    _curr->_prev->_prev->_next = _curr->_prev;
  }
}

int DLL::visit(){               // retruns data of current
return _curr->_data;
}
bool DLL::goHead(){
  _curr = _head;
  return (_curr != 0);
}
bool DLL::goTail(){
  _curr = _tail;
  return (_curr != 0);
}
bool DLL::goNext(){
  bool rt = false;
  if(_curr->_next){
    rt = true;
    _curr = _curr->_next;
  }
  return rt;
}
bool DLL::goPrev(){
bool rt = false;
  if(_curr->_prev){
    rt = true;
    _curr = _curr->_prev;
  }
  return rt;
}
bool DLL::isEmpty(){
return !_head;
}