How not to insert duplicate nodes in a bst

[techie929]

//Here is the function of inserting nodes.I tried using strcmp but its still not working.

void BinarySearchTree::insert(char* d)  
    {
            tree_node* t = new tree_node;
            tree_node* parent;
        strcpy(t->data,d);
            t->left = NULL;
            t->right = NULL;
            parent = NULL;
          // is this a new tree?
          if(isEmpty()) root = t;
          else
          {
                //Note: ALL insertions are as leaf nodes
                tree_node* curr;
                curr = root;
                // Find the Node's parent
            while(curr)
            {
				cout<<"current"<<curr->data<<endl;
                parent = curr;
				if(strcmp(t->data,curr->data)==0)
				{
					cout<<"duplicat nodes";
					exit(1);
				}
                if(strcmp(t->data,curr->data)>0) curr = curr->right;
                else curr = curr->left;
            }

            if(strcmp(t->data,parent->data)<0)
                   parent->left = t;
            else
                   parent->right = t;
          }
          count++;
    }

[mitrmkar]

//Here is the function of inserting nodes.I tried using strcmp but its still not working.

What do you mean by "still not working"?

Do you really want to use exit() there? I.e. your program gets terminated when duplicate data is encountered.

A suggestion regarding initialization of a tree_node

struct tree_node
{
  // default constructor
  tree_node() 
  : left(NULL), right(NULL)
  {
    // pointers are now initialized to NULL
  }
};

// So that would make somewhat cleaner code ..
tree_node* t = new tree_node;
// t->left and t->right are now automatically NULL
...

Then you might expand that even little more and also pass the data through the constructor.