Following C function can find the in-order successor of the root of a binary tree.
// step 1 of the above algorithm
if( n->right != NULL )
return minValue(n->right);
struct node *succ = NULL;
// Start from root and search for successor down the tree
while (root != NULL) {
if (n->data < root->data) {
succ = root;
root = root->left;
}
else if (n->data > root->data)
root = root->right;
else
break;
}
return succ;
}