...
string removedsmallest(StringTree * & t)
{ if (t->left == NULL)
  { string answer = t->data;
    t = t->right;
    return answer; }
  else
    return removedsmallest(t->left); }

void remove(StringTree * & t, string s)
{ if (t==NULL)
    return;
  else if (s == t->data)
  { if (t->left==NULL)
      t = t->right;
    else if (t->right==NULL)
      t = t->left;
    else
      t->data = removedsmallest(t->right); }
  else if (s < t->data)
    remove(t->left, s);
  else
    remove(t->right, s); }
...
...
    else if (command=="r")
    { string operand;
      cin >> operand;
      remove(tree, operand);
      cout << operand << " removed (if it was there)\n"; }
...