diff tree2/tree.c tree3/tree.c
3,4c3,4
<  *  (introduces typedef)
<  *
---
>  *  (store arbitrary 'things' using void*)
>  * 
15,16d14
< const int TREE_KEY_NOT_FOUND = -1; // used by tree_find()
< 
20c18
<   int data;		      // data for this item
---
>   void *data;		      // pointer to data for this item
31c29
< tree_new(const int key, const int data)
---
> tree_new(const int key, void *data)
51,52c49,50
<  * If the key is already in the tree, its datum is update with new data;
<  * the key should not be TREE_KEY_NOT_FOUND.
---
>  * If the key is already in the tree, its datum is update with new data.
>  * (The result is that old data pointer is lost.)
55c53
< tree_insert(tree_t *node, const int key, const int data)
---
> tree_insert(tree_t *node, const int key, void *data)
78c76
<  * return TREE_KEY_NOT_FOUND if key is not in tree.
---
>  * return NULL if key is not in tree.
80c78
< int 
---
> void *
84c82
<     return TREE_KEY_NOT_FOUND;
---
>     return NULL;
diff tree2/tree.h tree3/tree.h
3c3
<  *  (introduces typedef)
---
>  *  (store arbitrary 'things' using void*)
19c19
< tree_t *tree_new(const int key, int data);
---
> tree_t *tree_new(const int key, void *data);
25c25
<  * the key should not be TREE_KEY_NOT_FOUND.
---
>  * the key should not be tree_t_KEY_NOT_FOUND.
27c27
< tree_t *tree_insert(tree_t *root, const int key, const int data);
---
> tree_t *tree_insert(tree_t *root, const int key, void *data);
30c30
<  * return TREE_KEY_NOT_FOUND if key is not in tree.
---
>  * return tree_t_KEY_NOT_FOUND if key is not in tree.
32,33c32
< int tree_find(tree_t *root, const int key);
< extern const int TREE_KEY_NOT_FOUND;
---
> void *tree_find(tree_t *root, const int key);
diff tree2/treetest.c tree3/treetest.c
20a21,22
>   char datastring[] = "Test data";
> 
22,30c24,32
<   root = tree_insert(root, 3, 9);
<   root = tree_insert(root, 4, 9);
<   root = tree_insert(root, 1, 9);
<   root = tree_insert(root, 5, 9);
<   root = tree_insert(root, 6, 9);
<   root = tree_insert(root, 2, 9);
<   root = tree_insert(root, 8, 9);
<   root = tree_insert(root, 7, 9);
<   root = tree_insert(root, 0, 9);
---
>   root = tree_insert(root, 3, datastring);
>   root = tree_insert(root, 4, datastring);
>   root = tree_insert(root, 1, datastring);
>   root = tree_insert(root, 5, datastring);
>   root = tree_insert(root, 6, datastring);
>   root = tree_insert(root, 2, datastring);
>   root = tree_insert(root, 8, datastring);
>   root = tree_insert(root, 7, datastring);
>   root = tree_insert(root, 0, datastring);
32,33c34,35
<   printf("find %d returns %d\n", 4, tree_find(root, 4));
<   printf("find %d returns %d\n", 5, tree_find(root, 5));
---
>   printf("find %d returns %s\n", 4, tree_find(root, 4));
>   printf("find %d returns %s\n", 5, tree_find(root, 5));
36,37c38,39
<   root = tree_insert(root, 5, 99);
<   printf("find %d returns %d\n", 5, tree_find(root, 5));
---
>   root = tree_insert(root, 5, "new string");
>   printf("find %d returns %s\n", 5, tree_find(root, 5));