Grusel++ of the month

/******************************************************************************/
/*                                                                            */
/*                                                          FILE: january.cpp */
/*                                                                            */
/*  The treeterator                                                           */
/*  ===============                                                           */
/*                                                                            */
/*  Compiled and tested with Visual C++ 6.0                                   */
/*                                                                            */
/*  V1.00   31-JAN-2004   P. Tellenbach   http://www.heimetli.ch/             */
/*                                                                            */
/******************************************************************************/

#include <iostream>
#include <iterator>
#include <queue>
#include <algorithm>

template< class T >
class tree
{
  public:
    struct node
    {
       T    value ;
       node *left ;
       node *right ;
    } ;

    class iterator : public std::iterator<std::forward_iterator_tag, T>
    {
      public:
        bool operator==( const iterator &it )
        {
           return q == it.q ;
        }

        bool operator!=( const iterator &it )
        {
           return !(*this == it) ;
        }

        T &operator*()
        {
           return q.front()->value ;
        }

        T *operator->()
        {
           return &q.front()->value ;
        }

        iterator &operator++()
        {
           if( q.front()->left != NULL )
             q.push( q.front()->left ) ;

           if( q.front()->right != NULL )
             q.push( q.front()->right ) ;

           q.pop() ;

           return *this ;
        }

        iterator operator++( int )
        {
          iterator tmp( *this ) ;
          ++*this ;
          return tmp ;
        }

        iterator()
        {
        }

        iterator( node *pn )
        {
          q.push( pn ) ;
        }

      protected:
        std::queue<node *> q ; 
    } ;

    tree( node *r ) : root(r)
    {
    }

    iterator begin()
    {
      return iterator( root ) ;
    }

    iterator end()
    {
      return iterator() ;
    }

  protected:
    node *root ;
} ;    


tree<char>::node nD = { '\n', NULL, NULL } ;
tree<char>::node nC = { 'w',  NULL, NULL } ;
tree<char>::node nB = { '!',  NULL, NULL } ;
tree<char>::node nA = { ' ',  NULL, NULL } ;
tree<char>::node n9 = { ' ',  &nA,  &nB  } ;
tree<char>::node n8 = { 'l',  &n9,  &nC  } ;
tree<char>::node n7 = { 'd',  NULL, NULL } ;
tree<char>::node n6 = { 'l',  NULL, NULL } ;
tree<char>::node n5 = { 'o',  &n6,  &n7  } ;
tree<char>::node n4 = { 'r',  NULL, NULL } ;
tree<char>::node n3 = { 'o',  NULL, NULL } ;
tree<char>::node n2 = { 'l',  &n3,  &n4  } ;
tree<char>::node n1 = { 'e',  &n2,  &n5  } ;
tree<char>::node n0 = { 'H',  &n1,  &n8  } ;

int main()
{
  tree<char> tc( &n0 ) ;

  std::copy( tc.begin(), tc.end(), std::ostream_iterator<char>(std::cout) ) ;

  return 0 ;
}

Update 31. January 2024

This program compiles and runs without any changes.