// Teacher login and start Work() after login correctly static void Login() { int id; string idTry, passwd; bool loop = true; while (loop) { while (true) { Console.WriteLine( "////////////////////////////////////////////////////////////////////////////////////" + "\n" + "/* Welcome to Hebut Student Management System */" + "\n" + "/* */" + "\n" + "/* */" + "\n" + "/* Please Enter Your ID */" + "\n" + "/* */" + "\n" + "////////////////////////////////////////////////////////////////////////////////////" + "\n"); idTry = Console.ReadLine(); try { id = Int32.Parse(idTry); break; } catch (Exception e) { Console.WriteLine("Please enter a number !"); continue; throw; } } Console.WriteLine( "////////////////////////////////////////////////////////////////////////////////////" + "\n" + "/* Welcome to Hebut Student Management System */" + "\n" + "/* */" + "\n" + "/* */" + "\n" + "/* Please Enter Your Password */" + "\n" + "/* */" + "\n" + "////////////////////////////////////////////////////////////////////////////////////" + "\n"); passwd = Console.ReadLine(); loop = !itb.TeacherLogin(id, passwd); if (loop) { Console.WriteLine("ID error or password error"); } } Work(); }