public void Active() { ClassRoom Classes = new ClassRoom(); char askToContinue; var enterChoice = new EnterInformation(); var interFace = new InterfaceOfUser(); int optionItem; int isStudentExist; string userInput; do { interFace.MainMenu(); do { userInput = enterChoice.EnterUserInput(); optionItem = interFace.CheckAndReturn(userInput); } while (optionItem == -1); switch (optionItem) { case 1: Console.Clear(); Classes.GetInformationOfGroup(); break; case 2: Console.Clear(); isStudentExist = interFace.CheckStudentExist(Classes.Students.Count); if (isStudentExist != 0) { Classes.FuntionCheckInformation(); break; } else { break; } case 3: Console.Clear(); isStudentExist = interFace.CheckStudentExist(Classes.Students.Count); if (isStudentExist == 0) { break; } else { Classes.FindByID(); } break; case 4: Console.Clear(); isStudentExist = interFace.CheckStudentExist(Classes.Students.Count); if (isStudentExist == 0) { break; } else { Classes.FindStudentsHaveHighestAverageGrade(); } break; case 5: Console.Clear(); isStudentExist = interFace.CheckStudentExist(Classes.Students.Count); if (isStudentExist == 0) { break; } else { Classes.FindFailGrade(); } break; case 6: Console.Clear(); Classes.GetInformationASingleStudent(); break; case 7: Console.Clear(); isStudentExist = interFace.CheckStudentExist(Classes.Students.Count); if (isStudentExist == 0) { break; } else { Classes.CalculateAverages(); } break; case 8: Console.Clear(); isStudentExist = interFace.CheckStudentExist(Classes.Students.Count); if (isStudentExist == 0) { break; } else { Classes.DeleteStudentById(); } break; case 0: Console.Clear(); Console.Write("DONE"); break; default: Console.Clear(); Console.WriteLine("ERROR"); break; } askToContinue = interFace.CheckToContinue(optionItem); } while (optionItem != 0 && askToContinue == 'y'); }