C++/List/your list

Your own list

<source lang="cpp">

1. include <string>
2. include <iostream>
3. include <cassert>

using namespace std; class List; class Iterator; class Node { public:

  Node(string s);

private:

  string data;
  Node* previous;
  Node* next;

friend class List; friend class Iterator; }; class List { public:

  List();
  void push_back(string s);
  void insert(Iterator iter, string s);
  Iterator erase(Iterator i);
  Iterator begin();
  Iterator end();

private:

  Node* first;
  Node* last;

}; class Iterator { public:

  Iterator();
  string get() const;
  void next();
  void previous();
  bool equals(Iterator b) const;

private:

  Node* position;
  Node* last;

friend class List; }; Node::Node(string s) {

  data = s;
  previous = NULL;
  next = NULL;

} List::List() {

  first = NULL;
  last = NULL;

} void List::push_back(string s) {

  Node* newnode = new Node(s);
  if (last == NULL) 
  {  
     first = newnode;
     last = newnode;
  }
  else
  {  
     newnode->previous = last;
     last->next = newnode;
     last = newnode;
  }

} void List::insert(Iterator iter, string s) {

  if (iter.position == NULL)
  {  
     push_back(s);
     return;
  }
  Node* after = iter.position;
  Node* before = after->previous;
  Node* newnode = new Node(s);
  newnode->previous = before;
  newnode->next = after;
  after->previous = newnode;
  if (before == NULL) 
     first = newnode;
  else
     before->next = newnode;

} Iterator List::erase(Iterator i) {

  Iterator iter = i;
  assert(iter.position != NULL);
  Node* remove = iter.position;
  Node* before = remove->previous;
  Node* after = remove->next;
  if (remove == first)
     first = after;
  else
     before->next = after;
  if (remove == last)
     last = before;
  else
     after->previous = before;
  iter.position = after;
  delete remove;
  return iter;

} Iterator List::begin() {

  Iterator iter;
  iter.position = first;
  iter.last = last;
  return iter;

} Iterator List::end() {

  Iterator iter;
  iter.position = NULL;
  iter.last = last;
  return iter;

} Iterator::Iterator() {

  position = NULL;
  last = NULL;

} string Iterator::get() const {

  assert(position != NULL);
  return position->data;

} void Iterator::next() {

  assert(position != NULL);
  position = position->next;

} void Iterator::previous() {

  if (position == NULL)
     position = last;
  else 
     position = position->previous;
  assert(position != NULL);

} bool Iterator::equals(Iterator b) const {

  return position == b.position;

} int main() {

  List staff;
  staff.push_back("A");
  staff.push_back("B");
  staff.push_back("C");
  staff.push_back("D");
  Iterator pos;
  pos = staff.begin();
  pos.next();
  pos.next();
  pos.next();
  staff.insert(pos, "Reindeer, Rudolf");
  pos = staff.begin();
  pos.next();
  staff.erase(pos);
  for (pos = staff.begin(); !pos.equals(staff.end()); pos.next())
     cout << pos.get() << "\n";
  return 0;

}

 </source>