CMPS 223 Data Structures and Algorithms 
             Assignment 3: Doubly-Linked List & Iterator

I. Purposes:

    Understand doubly-linked list and know to design and implement simple structure
    so that use can traverse list items in forward and backward direction.

II. What you are going to do:

   Notice that no display(), and friend << operator defined. There are 4 class templates
   to implement:

       (1) Iterator -- a abstract template class for easy traversing list items.
       (2) DLList -- doubly-linked list template clas for list which has two inner classes.
       (3) Node   -- template class for node in list with double pointers and a data field.
       (4) DLListIterator -- an implementation of Iterator class.
       (*) You have to add iterator() in DLList class to make use of Iterator easy.
       (**) No display or << operator() should be dfiend.
       (***) The menu options are different from assignment 2.

   The 4 template classes are specified below, and feel free to add necessary functions.

   1. Define an abstract Iterator class template with following functions:
        template <class T>
	class Iterator {
            bool hasNext() const;
	    T    next() ;         // return the next list item
	}
       
   2. Define DLList class template with two inner class template inside list class:

   template <class T>
   class DLList {

     protected:

	class Node {
	   public:
	      T		data;
	      Node<T>	*next, *previous;
	      Node( const T & );
	      ~Node();
	};

	class DLListIterator : public Iterator<T> {
	    protected:
	       Node<T>	* cur;
	       bool	forward;
	    public:
	       DLListIterator( bool, Node<T> * );
	       bool	hasNext() const;
	       T	next() ;
	};

      	 int		count;
	 Node<T>	*head, * tail;

	public:

          DLList( );
          ~DLList();
          DLList( const DLList& );

	  Iterator<T> * iterator( bool fwd );

          bool    empty() const;

	  // Return this for cascade calls. (obj, pos)
          DLList& insert( const T & , int );

	  T       erase( int ) ;

     };

III. Use and make a few changes to your main program and menu for assignment one
     to test the singly linked list implementation.

       Menu for assigment 2 should be like the following:

              +=========================================+
              | HW3 : Doubly Linked List/Iterator       | 
              +=========================================+
              | C: Create one integer and one character |
              |    list, and insert 10 random values in |
              |    each list. The value ranges of lists |
              |    0 ... 99 and 'A' .. 'Z'.             |
              +-----------------------------------------+
              | F: Show list items in forward direction |
              |    using iterator.                      |
              +-----------------------------------------+
              | B: Show list items in backward direction|
              |    using iterator.                      |
              +-----------------------------------------+
              | A: Ask for a int and a char value,      |
              |    insert the values at random poistions|
              |    of the lists.                        |
              +-----------------------------------------+
              | D: Generate a random position, and      |
              |    remove values at the positions of the|
              |    int and char lists.                  |
              +-----------------------------------------+
              | H: Show this menu.                      |
              +-----------------------------------------+
              | Q: Exit program.                        |
              +-----------------------------------------+