diff tree6/tree.c tree7/tree.c
3c3
<  *  (version 6: introduce function pointer)
---
>  *  (version 7: add tree_delete)
37c37
< static void tree_print_helper(tree_t *tree, treenode_t *node, int depth, 
---
> static void tree_print_helper(tree_t *tree, treenode_t *node, int depth,
39a40,41
> static void tree_delete_helper(tree_t *tree, treenode_t *node,
> 			       void (*itemdelete)(void *data) );
184a187,219
> /**************** tree_delete() ****************/
> void 
> tree_delete(tree_t *tree, void (*itemdelete)(void *data) )
> {
>   if (tree != NULL) {
>     tree_delete_helper(tree, tree->root, itemdelete);
>   }
>   free(tree);
> }
> 
> /**************** tree_delete_helper() ****************/
> /* Recursive function to delete nodes of the tree.
>  */
> static void  // not visible outside this file
> tree_delete_helper(tree_t *tree, treenode_t *node,
> 		   void (*itemdelete)(void *data) )
> {
>   if (node != NULL) {
>     // delete the left subtree
>     tree_delete_helper(tree, node->left, itemdelete);
> 
>     // delete the right subtree
>     tree_delete_helper(tree, node->right, itemdelete);
>     
>     // delete the current node
>     if (itemdelete != NULL) {	 // but first...
>       (*itemdelete)(node->data); // delete its contents
>     }
>     free(node->key);
>     free(node);
>   }
>   return;
> }
diff tree6/tree.h tree7/tree.h
3c3
<  *  (version 6: introduce function pointer)
---
>  *  (version 7)
35a36,40
> /* Delete the whole tree, recursively.
>  * Provide a function that will delete an item.
>  */
> void tree_delete(tree_t *tree, void (*itemdelete)(void *data) );
> 
diff tree6/treetest.c tree7/treetest.c
46a47,50
> 
>   printf("\ndelete the tree...");
>   tree_delete(tree, NULL);
>   printf("done\n");