postorder traversal without recursion in a binary tree

#include<iostream>
#include<stack>
using namespace std;

class Node{
  public:
      int data;
      Node *left,*right;
      Node(int key){
        data=key;
        left=NULL;
        right=NULL;
        }
  };

void Postorder(Node* root){
  if(root==NULL)
    return;
  stack<Node*>s;
  stack<int>out;
  s.push(root);
  while(!s.empty()){
    Node* temp=s.top();
    s.pop();
    out.push(temp->data);
    if(temp->left)
        s.push(temp->left);
    if(temp->right)
        s.push(temp->right);
    }
  while(!out.empty()){
    cout<<" "<<out.top();
    out.pop();
    }
  }

int main(){
  Node* root=NULL;
  Node* newnode=new Node(1);
  root=newnode;
  root->left=new Node(9);
  root->right=new Node(3);
  (root->left)->left=new Node(2);
  (root->right)->right=new Node(4);
  Postorder(root);
  return 0;
  }