Data Structure Binary Tree: Inorder Tree Traversal without Recursion

http://www.geeksforgeeks.org/inorder-tree-traversal-without-recursion/

 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <queue>
 #include <stack>
 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) { }
 };
 
 void print(node *root) {
     stack<node*> S;
     if (!root) return;
     node *cur = root;
     while () {
         if (cur) {
             S.push(cur);
             cur = cur->left;
         }
         else if (!S.empty()) {
             cur = S.top();
             S.pop();
             cout << cur->data << " ";
             cur = cur->right;
         }
         else break;
     }
 }
 
 int main() {
     struct node* root = new node();
     root->left = new node();
     root->right = new node();
     root->left->left = new node();
     root->left->right = new node();
     print(root);
     return ;
 }