Get sum of entered values using List collection

iJunior_C#_Lesson_34

using System.Collections;
using System.Diagnostics;

namespace iJuniorPractice;

class Program
{
    static void Main(string[] args)
    {
        const string SumCommand = "Sum";
        const string ExitCommand = "Exit";
        
        List<int> numbers = new List<int>();
        string userInput;
        bool isWork = true;

        while (isWork)
        {
            Console.WriteLine($"Eneter values " +
                              $"or \"{SumCommand}\" to get sum of the entered values " +
                              $"or \"{ExitCommand}\" to exit program");

            userInput = Console.ReadLine();
            
            switch (userInput)
            {
                case SumCommand:
                    Console.WriteLine(CalculateSum(numbers));
                    break;
                
                case ExitCommand:
                    Console.WriteLine("Goodbye!");
                    isWork = false;
                    break;
                
                default:
                    numbers.Add(ReadInt(userInput));
                    break;
            }

            Console.WriteLine("Enter any key to continue...");
            Console.ReadKey();
            Console.Clear();
        }
    }

    static int CalculateSum(List<int> numbers)
    {
        int sum = 0;
        
        foreach (var number in numbers)
        {
            sum += number;
        }

        return sum;
    }

    static int ReadInt(string input)
    {
        int number;
        
        while (int.TryParse(input, out number) == false)
        {
            Console.WriteLine("Incorrect value!");
            Console.Write("Enter value: ");
            input = Console.ReadLine();
        }

        return number;
    }
}