Data Structure Binary Search Tree: Find k-th smallest element in BST (Order Statistics in BST)

http://www.geeksforgeeks.org/find-k-th-smallest-element-in-bst-order-statistics-in-bst/

 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <queue>
 #include <stack>
 #include <string>
 #include <fstream>
 #include <map>
 using namespace std;

 struct node {
     int data;
     struct node *left, *right;
     node() : data(), left(NULL), right(NULL) { }
     node(int d) : data(d), left(NULL), right(NULL) { }
 };

 node *insert(node *root, int key) {
     if (!root) return new node(key);
     if (root->data > key) root->left = insert(root->left, key);
     else root->right = insert(root->right, key);
     return root;
 }

 void prints(node *root) {
     if (!root) return;
     prints(root->left);
     cout << root->data << " ";
     prints(root->right);
 }

 node *k_smallest(node *root, int k) {
     stack<node*> S;
     while () {
         while (root) {
             S.push(root);
             root = root->left;
         }
         if (!S.empty()) {
             root = S.top();
             S.pop();
             if (k- == ) return root;
             k--;
             root = root->right;
         }
         else break;
     }
     return NULL;
 }

 int main() {
     node *root = NULL;
     root = insert(root, );
     insert(root, );
     insert(root, );
     insert(root, );
     insert(root, );
     insert(root, );
     insert(root, );
     if (k_smallest(root, )) cout << k_smallest(root, )->data << endl;
     else cout << "No node" << endl;
     return ;
 }