maintain index to count number of nodes processed so far
int count = 0 ; Node * res = kthSmallest ( root , k ) ; if ( res == NULL ) cout << " There ▁ are ▁ less ▁ than ▁ k ▁ nodes ▁ in ▁ the ▁ BST " ; else cout << " K - th ▁ Smallest ▁ Element ▁ is ▁ " << res -> data ; }