static void Main(string[] args) { Book book = new Book("Ade"); while (true) { Console.WriteLine("Please enter grade or 'q' to quit: "); var gradeInput = Console.ReadLine(); try{ var gradeInt = double.Parse(gradeInput); book.AddGrades(gradeInt); }catch (Exception FormatException) { Console.WriteLine(FormatException.Message); } if (gradeInput == "q") { break; } } book.DisplayStatisticsSummary(); }