using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var a = new List<int> { 1, 2, 3 };

        Console.WriteLine(string.Join(", ", a.Select(i => i.ToString())));

        Foo(a);

        Console.WriteLine(string.Join(", ", a.Select(i => i.ToString())));

        Bar(a);

        Console.WriteLine(string.Join(", ", a.Select(i => i.ToString())));

    }

    public static void Foo(IEnumerable<int> a)

    {

        var aList = a.ToList();

        aList.Add(4);

    }

    public static void Bar(List<int> a)

    {

        a.Add(5);

    }

}