Code to implement a tree (excercise done in cdac)

#include 
using namespace std;

class tree;

class node
{
private:
 int data;
 node *left;
 node *right;
public:
 node();
 node(int val);
 friend class tree;
};

 node::node()
  : data(0), left(NULL), right(NULL)
 {
 }
 node::node(int val)
  : data(val), left(NULL), right(NULL)
 {
 }

class tree
{
private:
 node *root;
public:
 // construct & destruct
 tree();
 ~tree();
 // creation
 void add_node(int val);
 // deletion
 void del_node(int val);
 void clear(node *trav);
 void clear()
 {
  clear(root);
  root = NULL;
 }
 // display
 void inorder(node *trav);
 void inorder()
 {
  inorder(root);
 }
 void preorder(node *trav);
 void preorder()
 {
  preorder(root);
 }
 void postorder(node *trav);
 void postorder()
 {
  postorder(root);
 }
 // others
 int height(node *trav);
 int height()
 {
  int ht = height(root);
  return ht;
 }
 node* search(int val);
};


 // construct & destruct
 tree::tree()
 {
  root = NULL;
 }
 tree::~tree()
 {
  clear();
 }
 // creation
 void tree::add_node(int val)
 {
  node *newnode = new node(val);
  if(root == NULL) // tree is empty
   root = newnode;
  else // tree is not empty
  {
   node *trav = root;
   while(1)
   {
    if(val < trav->data)
    { // add node to the left
     if(trav->left == NULL) 
     {
      trav->left = newnode;
      break;
     }
     else
      trav = trav->left;
    }
    else
    { // add node to the right
     if(trav->right == NULL)
     {
      trav->right = newnode;
      break;
     }
     else
      trav = trav->right;
    }
   }
  }
 }
 // deletion
 void tree::del_node(int val)
 {
 }
 void tree::clear(node *trav)
 {
  if(trav==NULL)
   return;
  clear(trav->left);
  clear(trav->right);
  delete trav;
 }
 // display
 void tree::inorder(node *trav)
 {
  if(trav==NULL)
   return;
  inorder(trav->left);
  cout << trav->data << " ";
  inorder(trav->right);
 }
 void tree::preorder(node *trav)
 {
  if(trav==NULL)
   return;
  cout << trav->data << " ";
  preorder(trav->left);
  preorder(trav->right);
 }
 void tree::postorder(node *trav)
 {
  if(trav==NULL)
   return;
  postorder(trav->left);
  postorder(trav->right);
  cout << trav->data << " ";
 }
 // others
 int tree::height(node *trav)
 {
  if(trav==NULL)
   return 0;
  int ht_left = height(trav->left);
  int ht_right = height(trav->right);
  int max = ht_left > ht_right ? ht_left : ht_right;
  return max+1;
 }
 node* search(int val)
 {
  return NULL;
 }

int main()
{
 tree t;
 t.add_node(10);
 t.add_node(5);
 t.add_node(3);
 t.add_node(15);
 t.add_node(18);
 t.add_node(8);
 t.add_node(12);

 cout << "pre order : ";
 t.preorder();
 cout << endl;

 cout << "in order : ";
 t.inorder();
 cout << endl;
 
 cout << "post order : ";
 t.postorder();
 cout << endl;

 int h = t.height();
 cout << "height : " << h << endl;
 return 0;
}