Mirror a BST

/*

 Change a tree so that the roles of the
 left and right pointers are swapped at every node.
 So the tree...
       4
      / \
     2   5
    / \
   1   3

 is changed to...
       4
      / \
     5   2
        / \
       3   1
*/

void mirror(struct node* node) {
  if (node==NULL) {
    return;
  }
  else {
    struct node* temp;

    // do the subtrees
    mirror(node->left);
    mirror(node->right);

    // swap the pointers in this node
    temp = node->left;
    node->left = node->right;
    node->right = temp;
  }
}