task25

using System;
using System.Collections.Generic;

public class Program
{
    public static void Main()
    {
        List<int> listNumbers = new List<int>();

        long sumNumbers = 0;

        int inputNumber;
        string inputString = null;

        bool isRun = true;
        bool isNumber = true;

        while (isRun)
        {
            inputNumber = InputNumber(ref isNumber, ref inputString);

            if (isNumber)
            {
                sumNumbers += inputNumber;
                listNumbers.Add(inputNumber);
            }
            else
            {
                switch (inputString)
                {
                    case "sum":
                        Console.WriteLine($"The sum of numbers is : {sumNumbers}");
                        break;
                    case "exit":
                        isRun = false;
                        break;
                    default:
                        Console.WriteLine("You write wrong number or command.");
                        break;
                }
            }
        }
    }

    public static int InputNumber(ref bool isNumber, ref string inputString)
    {
        int inputNumber;

        Console.WriteLine("Input a number or a command: ");
        inputString = Console.ReadLine();
        isNumber = int.TryParse(inputString, out inputNumber);

        return inputNumber;
    }
}