cout << "Book 1 title : " << Book1.title <<endl;
   cout << "Book 1 author : " << Book1.author <<endl;
   cout << "Book 1 subject : " << Book1.subject <<endl;
   cout << "Book 1 id : " << Book1.book_id <<endl;
   // Print Book2 info
   cout << "Book 2 title : " << Book2.title <<endl;
  : " << Book2.subject <<endl;
   cout << "Book 2 id : " << Book2.book_id <<endl;
   return 0;