Answer to Question 37A-3

  void addup(ConstTree T, int& v)
  {
    if(T != NULL)
    {
      v += T->item;
      addup(T->left,  v);
      addup(T->right, v);
    }
  }

  int sum(Tree T)
  {
    int v = 0;
    addup(T, v);
    return v;
  }