Binary tree with preorder ,inorder ,postorder traversing

/*binary tree with pre,in,post order traversing
compiler- Turbo c++     author- Mangilal Sharma
--------------------------------------------------------*/
#include<iostream.h>
#include<conio.h>
#include<stdlib.h>

struct b_node
{
 int data;
 struct b_node *left;
 struct b_node *right;
}*root;

class binary
{
 public:
 int count;
 struct b_node *insert(struct b_node *root,int num);
 void preorder(struct b_node *root);
 void inorder(struct b_node *root);
 void postorder(struct b_node *root);
 binary();
};

struct b_node *binary::insert(struct b_node *root,int num)
{
 if(root==NULL)
 {
  root=(struct b_node *)malloc(sizeof(struct b_node));
  root->data=num;
  root->left=NULL;
  root->right=NULL;
  count++;
 }
 else
 {
  if(count%2==0)
  {
   root->left=insert(root->left,num);
  }
  else
  {
   root->right=insert(root->right,num);
  }
 }
 return(root);
}

void binary::preorder(struct b_node *root)
{
 if(root!=NULL)
 {
  cout<<root->data;
  preorder(root->left);
  preorder(root->right);
 }
}

void binary::inorder(struct b_node *root)
{
 if(root!=NULL)
 {
  inorder(root->left);
  cout<<root->data;
  inorder(root->right);
 }
}

void binary::postorder(struct b_node *root)
{
 if(root!=NULL)
 {
  postorder(root->left);
  postorder(root->right);
  cout<<root->data;
 }
}

binary::binary()
{
 struct b_node *root=NULL;
 count=-1;
 int choice,num;
 do
 {
  cout<<"\n\t\t\tBinary Tree\n";
  cout<<"\t\t1. Insert node in tree\n";
  cout<<"\t\t2. Preorder Traversal\n";
  cout<<"\t\t3. Inorder traversal\n";
  cout<<"\t\t4. Postoder Traversl\n";
  cout<<"\t\t5. Main menu\n";
  cout<<"\t\t6. Exit\n";
  cout<<"\t\tEnter ur choice=";
  cin>>choice;
  switch(choice)
  {
   case 1:
   cout<<"enter No. to add in tree & -999 to exit\n";
   cin>>num;
   while(num!=-999)
   {
    root=insert(root,num);
    cin>>num;
   }break;
   case 2:
   cout<<"Preorder Traversing\n";
   preorder(root);break;
   case 3:
   cout<<"Inorder Traversing\n";
   inorder(root);break;
   case 4:
   cout<<"Postorder Traversing";
   postorder(root);break;
   case 5: return;
   case 6: exit(1);
   default:cout<<"Wrong Choice";
  }
 }while(1);
}
/*=========================13Nov.,2010=============================*/