main.cpp

#include <iostream>
using namespace std;

struct Node {
    int data;
    Node* left_link;
    Node* right_link;
};

/* method declarations */
Node* get_new_node(int data);
void insert(int data, Node* &root_address);
bool is_present(int data, Node* root_address);

Node* root_address = NULL; //Not best practice but I have made this global for ease of use.

int main() {
  insert(15, root_address);
  insert(10, root_address);
  insert(20, root_address);
  insert(18, root_address);

  cout<<is_present(10, root_address)<<endl;
  cout<<is_present(12, root_address)<<endl;
  cout<<is_present(18, root_address)<<endl;
}

void insert(int data, Node* &root_address) {

  if (root_address == NULL) {
    root_address = get_new_node(data);
  }
  else if (data <= root_address -> data) {
    insert(data, root_address -> left_link);
  }
  else {
    insert(data, root_address -> right_link);
  }

}

Node *get_new_node(int data) {

  Node* new_node_address = new Node();
  new_node_address -> data = data;
  new_node_address -> left_link = NULL;
  new_node_address -> right_link = NULL;
  return new_node_address;

}

bool is_present(int data, Node* root_address) {
  bool search_result;

  if (root_address == NULL) {
    search_result = false;
  }
  else if (data == root_address -> data) {
    search_result = true;
  }
  else if (data < root_address -> data){
    search_result = is_present(data, root_address -> left_link);
  }
  else if (data > root_address -> data) {
    search_result = is_present(data, root_address -> right_link);
  }
  else {
    search_result = false;
  }
  return search_result;
}