zig zag traversal 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 ZigZagTraversal(Node* root){
 if(root==NULL)
    return;
 stack<Node*>s1;
 stack<Node*>s2;
 s1.push(root);
 while(!s1.empty()||!s2.empty()){
    while(!s1.empty()){
      Node *temp=s1.top();
      cout<<" "<<temp->data;
      s1.pop();
      if(temp->left!=NULL)
        s2.push(temp->left);
      if(temp->right!=NULL)
        s2.push(temp->right);
      }
    while(!s2.empty()){
      Node *temp=s2.top();
      cout<<" "<<temp->data;
      s2.pop();
      if(temp->right!=NULL)
        s1.push(temp->right);
      if(temp->left!=NULL)
        s1.push(temp->left);
      }
    }
 }

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)->left=new Node(8);
  (root->right)->right=new Node(4);
  ZigZagTraversal(root);
  return 0;
  }