Preorder Traversal of Threaded Binary Tree

See here what is preorder traversal ?

Algorithm

Make root node as current node.

Until current node is not NULL  

          a)Print current key.

          b)if current node has left child,then make left child as current node.

          c)else if current node has right child then make right child as current node.

          d)else
                  Until right thread exists for current node
                       Traverse up the right threads and update current.
                  if current node  = last node.STOP.
                  else make right child of current node as current.

Code

void preorder(node* root)
{
    node* curr = root;

    while(curr!=NULL)
    {
        printf("%d ",curr->key);

        if(curr->left!=NULL)
            curr=curr->left;

        else if(curr->is_rchild==1)
            curr=curr->right;

        else
        {
            while(curr->right!=NULL && curr->is_rchild==0)      //right thread exists
                curr=curr->right;

            if(curr->right == NULL)                            //last node
                break;
            else
                curr=curr->right;

        }
    }
}

Code Tracing