using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string[] contactName = null;

        //contactName.Add = "t";

        var list = new List<string>() { "one", "two" };

​

        list.Insert(0, "zero");

        list.Add("three");

        string x = string.Join(",", list);

        Console.WriteLine(x);

        Console.WriteLine(list[0]);

        //string newList = String.Join("',", list);

        string newList = String.Join(",", list.Select(x => $"'{x}'"));

        Console.WriteLine(newList);

    }

}