Non-recursive tree traversals

Was asked recently by a friend to try this out. They are all almost the same except that postorder is a bit tricky. And do drop a gentle and kind comment if there are any mistakes :D

So here goes ...

Inorder:
--------
inorder(node *ptr)
{
  lptr = ptr;
  while(lptr!=NULL) {
    stack.push(lptr);
    lptr = lptr->left;
  }

  while(!stack.empty()) {
    p = stack.pop();
    print(p->data);

    q = p->right;
    while(q!=NULL) {
      stack.push(q);
      q = q->left;
    }
  }
}


Preorder:
---------
preorder(node *ptr)
{
  lptr = ptr;
  while(lptr!=NULL) {
    print(lptr->data);
    stack.push(lptr);
    lptr = lptr->left;
  }

  while(!stack.empty()) {
    p = stack.pop();
    q = p->right;
    while(q!=NULL) {
      print(q->data);
      stack.push(q);
      q = q->left;
    }
  }
}


Postorder:
----------
postorder(node *ptr)
{
  lptr = ptr;
  while(lptr!=NULL) {
    stack.push(lptr);
    lptr = lptr->left;
  }

  while(!stack.empty()) {
    p = stack.pop();
  
    if(p->right==NULL || p->right==last) {
      print(p->data);
    }
    else {
      q = p->right;

      // if right child exists, push back the parent node onto the stack
      if(q!=NULL)
        stack.push(p);

      while(q!=NULL) {
        stack.push(q);
        q = q->left;
      }
    }
    last = p;
  }
}