threaded binary tree. can't find out the error (in next_ordr fnc.) . Help!

[san467]

#include <iostream>

using namespace std;
struct node
{
node * right, *left;
int info;
bool lthread,rthread;   
};
class tree
{
private:
node *temp,*current;    

public:
node *root,*Dummy;
void insert(node*,int); 

void inorder(node*) ;

node* next_node(node* );

tree()
{ temp=root=current=NULL;
Dummy=new node;
  Dummy->left=root;
  Dummy->right=Dummy;
    Dummy->rthread= Dummy->lthread=false;
}



} ;
void tree::insert (node *temp,int key)
{
 if(root == NULL)
 {root = new node;
  root->info=key;
  root->left=root->right= Dummy;
  root->rthread=root->lthread=true;
  return;
 }
    if(key<temp->info)
    {if(!temp->lthread)
       insert(temp->left,key);
       else
      {
       current=new node;
       current->info=key;
       current->right=temp;
       current->left=temp->left;
       current->lthread=current->rthread=true;
       temp->left=current;
       temp->lthread=false;
       //cout<<"left child";
       return;}
    }
    if(key>temp->info)
    {if(!temp->rthread)
       {//cout<<"right;";
        insert(temp->right,key);
         }
     else 
     { //cout<<"right child";  
       current=new node;
       current->info=key;
       current->right=temp;
       current->left=temp->right;
       current->lthread=current->rthread=true;
       temp->right=current;
       temp->rthread=false;
       return;
    }
 }
 if(key==temp->info)
   {
    cout<<"dplicte.entr again"; cin>>key;
    insert(temp,key);
   }
}

node* tree :: next_node(node* temp)
{ 
    if(temp->rthread)
    { //cout<<"enterd if"; 
    return temp->right;
    }


       temp=temp->right;
    while(!temp->lthread )
       {//cout<<"enterd w2"; 
        temp=temp->left;   // the problem is in this statement or whenever i use temp->left
        }

        return temp;
}

void tree::inorder(node* temp)
{  int i=0;

  while(next_node(temp)!=Dummy)
{  
    cout<<"node"<<i++<<endl;
    cout<<temp->info<<endl;}
    return;
}


//........................................

int main( ) {
    tree obj;
    int n;
    for(int i=0;i<5;i++)
    {  cin>>n;
      obj.insert(obj.root,n);
}

cout<<"output\n";
obj.inorder(obj.Dummy);

    return 0;
}