using System;

using System.Runtime;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var list = new List<MyThread>();

        list.Add(new MyThread());

        list.Add(new MyThread());

        list.Add(new MyThread());

        list.Add(new MyThread());

        foreach (var t in list)

        {

            t.i = 3;

        }

​

        for (int i = 0; i < list.Count; i++)

        {

            if (i % 2 == 0)

                list[i] = null;

        }

​

        foreach (var t in list)

        {

            Console.WriteLine(t == null ? -1 : t.i);

        }

    }

}

​

public class MyThread

{

    public int i { get; set; }

}