Unit_34

using System;
using System.Collections.Generic;

namespace Ijunior
{
    internal class Program
    {
        static void Main(string[] args)
        {
            const string CommandSum = "sum";
            const string CommandExit = "exit";

            List<int> numbers = new List<int>();
            string userInput;
            bool isWork = true;

            while (isWork)
            {
                ShowList(numbers);

                Console.Write($"\n\nВведите число или {CommandSum} для суммы и {CommandExit} для выхода: ");
                userInput = Console.ReadLine();

                if (userInput.ToLower() == CommandSum)
                {
                    Console.WriteLine("Сумма чисел списка: " + CountSum(numbers));
                    Console.ReadKey();
                }
                else if (userInput.ToLower() == CommandExit)
                {
                    isWork = false;
                }
                else
                {
                    if (int.TryParse(userInput, out int number))
                    {
                        numbers.Add(number);
                    }
                }

                Console.Clear();
            }
        }

        static void ShowList(List<int> numbers)
        {
            if (numbers.Count > 0)
            {
                foreach (int number in numbers)
                {
                    Console.Write(number + " ");
                }
            }
            else
            {
                Console.Write("Список пуст");
            }
        }

        static int CountSum(List<int> numbers)
        {
            int sum = 0;

            foreach (int number in numbers)
            {
                sum += number;
            }

            return sum;
        }
    }
}