public static void MenuExercises() { CreateExercisesList(); Console.WriteLine("> Menu Exercises: "); foreach (var exercise in Exercises) { Console.WriteLine(exercise); } Console.WriteLine("Write the number of the example you want to see:"); var input = Console.ReadLine(); var select = 0; if (input == null) { Console.WriteLine("You must choose."); MenuExercises(); return; } select = Int32.Parse(input); switch (select) { case 0: Menu(); break; case 1: Console.Clear(); Exercise1.Run(); break; default: Console.Clear(); Console.WriteLine("That exercise doesn't exist."); MenuExercises(); break; } }