Implementing class BinaryTreeNavigator

template < typename T >
bool BinaryTreeNavigator<T>::HasParent () const
{
  if (currNode_ != 0 && currNode_ -> parent_ != 0)
    return 1;
  return 0;
}

template < typename T >
bool BinaryTreeNavigator<T>::HasLeftChild () const
{
  if (currNode_ != 0 && currNode_ -> lchild_ != 0)
    return 1;
  return 0;
}

template < typename T >
bool BinaryTreeNavigator<T>::IsLeftChild () const
{
  if (currNode_ != 0 && currNode_ -> parent_ != 0 && currNode_ == currNode_ -> parent_ -> lchild_)
    return 1;
  return 0;
}

template < typename T >
bool BinaryTreeNavigator<T>::Valid() const
{
  return currNode_ != 0;
}

template < typename T >
T& BinaryTreeNavigator<T>::Retrieve()
{
  if (currNode_ == 0)
  {
    // error
  }
  return (currNode_->value);
}

template < typename T >
BinaryTreeNavigator<T> & BinaryTreeNavigator<T>::operator ++()
{
  if (currNode_ != 0)
  {
    currNode_ = currNode_ -> lchild_;
  }
  return *this;
}

template < typename T >
BinaryTreeNavigator<T> & BinaryTreeNavigator<T>::operator ++(int)
{
  if (currNode_ != 0)
  {
    currNode_ = currNode_ -> rchild_;
  }
  return *this;
}

template < typename T >
BinaryTreeNavigator<T> & BinaryTreeNavigator<T>::operator --()
{
  if (currNode_ != 0)
  {
    currNode_ = currNode_ -> parent_;
  }
  return *this;
}