C++ program that uses non-recursive functions to traverse a binary tree in Post-order

#include<iostream.h>
#include<conio.h>
#include<stdlib.h>
 
class node
{
public:
class node *left;
class node *right;
int data;
};
 
class tree: public node
{
public:
int stk[50],top;
node *root;
tree()
{
root=NULL;
top=0;
}
void insert(int ch)
{
node *temp,*temp1;
if(root== NULL)
{
root=new node;
root->data=ch;
root->left=NULL;
root->right=NULL;
return;
}
temp1=new node;
temp1->data=ch;
temp1->right=temp1->left=NULL;
temp=search(root,ch);
if(temp->data>ch)
temp->left=temp1;
else
temp->right=temp1;
 
}
node *search(node *temp,int ch)
{
if(root== NULL)
{
cout <<"no node present";
return NULL;
}
if(temp->left==NULL && temp->right== NULL)
return temp;
 
if(temp->data>ch)
{  if(temp->left==NULL) return temp;
search(temp->left,ch);}
else
{ if(temp->right==NULL) return temp;
search(temp->right,ch);
 
}              }
 
void display(node *temp)
{
if(temp==NULL)
return ;
display(temp->left);
cout<<temp->data << " ";
display(temp->right);
}
void postorder( node *root)
{
node *p;
p=root;
top=0;
 
while(1)
{
while(p!=NULL)
{
stk[top]=p->data;
top++;
if(p->right!=NULL)
stk[top++]=-p->right->data;
p=p->left; 
}
while(stk[top-1] > 0 || top==0)
{
if(top==0) return;
cout << stk[top-1] <<" ";
p=pop(root);
}
if(stk[top-1]<0)
{
stk[top-1]=-stk[top-1];
p=pop(root);
}	}
 
}
node * pop(node *p)
{
int ch;
ch=stk[top-1];
if(p->data==ch)
{
top--;
return p;
}
if(p->data>ch)
pop(p->left);
else
pop(p->right);
}
};
void main()
{
tree t1;
int ch,n,i;
clrscr();
while(1)
{
cout <<"\n1.INSERT\n2.DISPLAY 3.POSTORDER TRAVERSE\n4.EXIT\nEnter your choice:";
cin >> ch;
switch(ch)
{
case 1:   cout <<"enter no of elements to insert:";
cout<<"\n enter the elements";
cin >> n;
for(i=1;i<=n;i++)
{  cin >> ch;
t1.insert(ch);
}
break;
case 2:   t1.display(t1.root);break;
case 3:   t1.postorder(t1.root); break;
case 4:   exit(1);
}
}
}