static void Main(string[] args) { Console.WriteLine("Input expression"); string str = Console.ReadLine(); Console.WriteLine("Choose arrayStack (0) or stack (1)"); int i = int.Parse(Console.ReadLine()); if (i == 0) { var calculatorArray = new StackCalculator(str, new StackArray()); calculatorArray.Calculate(); return; } var calculator = new StackCalculator(str, new Stack()); calculator.Calculate(); }