Binary Search Tree Insertion C without recursion

Question

I am new to the page and I am really stuck at my university's homework to recreate a function that inserts nodes to the tree without Recursion. I have been given the Recursive method and I need to convert it to Iterative. This is the given Recursive Code:

TreeNode *InsertTree(TreeNode *root, TreeNode *newnode)
{
   if (!root)
   {
      root = newnode;
      root->left = root->right=NULL;
   }
   else if (newnode->entry < root->entry)
   {  
      root->left = InsertTree(root->left, newnode);
   }
   else
   {
      root->right = InsertTree(root->right, newnode);
   }
   return root;
}

and I made this one:

TreeNode *InsertTree(TreeNode *root, TreeNode *newnode)
{
   if (!root)
   {
      root = newnode;
      root->left = root->right=NULL;
   }  
   else 
   {
      TreeNode * temp = root, *prev = NULL;

      while(temp)
      {
        if (temp->entry < newnode->entry)
          temp = temp->right;
        else
          temp = temp->left;
      }
      newnode;
      temp->left = temp->right = NULL;
   }
   return root;
}

it works for the first elements but it doesn't save the rest elements. Any ideas? Thanks in advance

Solution

The (un)usage of prev indicates the awareness that the recursive results need to be patched. As already a solution is given by others, here the "ideal" solution, using pointer aliases.

   TreeNode **current = &root;
   while (*current)
   {
       if (newnode->entry < (*current)->entry)
       {
           current = &(*current)->left;
       }
       else
       {
           current = &(*current)->right;
       }
   }
   *current = newnode;
   newnode->left = newnode->right = NULL;
   return root;

current will at the end point to root, or a left/right of a node; being null.

Note that this usage of aliases does not exist in some other languages like java. One of the very few advantages of C.

The & prefix-operator takes the address of the variable.

Comments

[Admin]

A ( is missing in the second to last line of your code.

[Ilias Mentz]

@JoopEggen That is working perfect thank you very much for help!