static void Main(string[] args) { SimpleCalc sc = new SimpleCalc(); FormulaCalc fc = new FormulaCalc(); Console.WriteLine("Press 1 to do simple calculations or 2 to enter a formula"); int input = Convert.ToInt32(Console.ReadLine()); switch (input) { case 1: Console.Clear(); sc.SimpleCalculator(); break; case 2: Console.Clear(); fc.AdvancedCalculator(); break; default: Console.WriteLine("Not a valid option"); break; } }