/*
 Given a binary tree, return true if a node
 with the target data is found in the tree. Recurs
 down the tree, chooses the left or right
 branch by comparing the target to each node.
*/
bool int lookup(struct node* node, int target) {
  // 1. Base case == empty tree
  // in that case, the target is not found so return false
  if (node == NULL) {
    return(false);
  }
  else {
    // 2. see if found here
    if (target == node->data) return(true);
    else {
      // 3. otherwise recur down the correct subtree, this is hightlight. 
      if (target < node->data) return(lookup(node->left, target));
      else return(lookup(node->right, target));
    }
  }
}