c - Difference between two recursive algorithms to delete a binary search tree -

i have question these 2 algorithms:

this works normally:

node* deletetree(node* root) {     if(root != null)     {        deletetree(root->left);        deletetree(root->right);        deallocatenode(root);     }     return root=null; } 

this nope:

void deletetree(node* root) {    if(root != null)    {       deletetree(root->left);       deletetree(root->right);       deallocatenode(root);    }    root=null; } 

why? need set root null node pointer after delete of bst not point memory not allocated. prefer second algorithm because recall of function more intuitive.

theoretically, 2 algorithms equivalent if use second algorithm , try print bst, program goes in loop.

when have node *root , assign node = null won't affect value in exterior. if want modify pointer value, you'll have pass double pointer.

something like:

void deletetree(node** root) {    if(*root != null)    {       deletetree(&((*root)->left));       deletetree(&((*root)->right));       deallocatenode(*root);    }    *root = null; } 

but don't think need assign node = null since free it. so, can assign node = null after call deletetree , won't need mess double pointer.