Shell

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ShellTest
{

    class ExitCommand : ShellDLL.Command
    {
        CalculatorShell calcShell;

        public ExitCommand(CalculatorShell calcShell) :base("exit")
        {
            this.calcShell = calcShell;
        }

        public override bool Execute(params string[] args)
        {
            if (args.Length != 0)
            {
                return false;
            }

            calcShell.Exit(0);
            return true;
        }
    }

    class PlusCommand : ShellDLL.Command
    {
        CalculatorShell calcShell;

        public PlusCommand(CalculatorShell calcShell) : base("+")
        {
            this.calcShell = calcShell;
        }

        public override bool Execute(params string[] args)
        {
            if (args.Length != 0)
            {
                return false;
            }
            double number;
            if (!double.TryParse(args[0], out number))
            {
                return false;
            }
            calcShell.Result += number;
            calcShell.Format(calcShell.ToString());
            return true;
        }

    }

    class CalculatorShell : ShellDLL.Shell
    {
        public double Result { get; set; }

        public override string ToString()
        {
            return string.Format($"{Result:F2}");
        }

        protected override void Init()
        {
            base.Init();
            Result = 0.0;

            Format($"{Result:F2}");
        }

        public CalculatorShell()
        {
            AddCommand(new ExitCommand(this));
            AddCommand(new PlusCommand(this));
        }
    }

    public class Program
    {
        public static void Main(string[] args)
        {
            ShellDLL.Shell sh = new CalculatorShell();
            sh.ReadEvalPrint();
        }
    }
}