using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    private static void UseList(List<int> array)

    {

        var watch = new System.Diagnostics.Stopwatch();

        watch.Start();

        int sum = 0;

        foreach (var num in array)

        {

            sum += num;

        }

        watch.Stop();

        Console.WriteLine("List " + watch.ElapsedMilliseconds);

    }

    private static void UseEnumerable(IEnumerable<int> array)

    {

        var watch = new System.Diagnostics.Stopwatch();

        watch.Start();

        int sum = 0;

        foreach (var num in array)

        {

            sum += num;

        }

        Console.WriteLine("Enumerable " + watch.ElapsedMilliseconds);

    }

    public static void Main()

    {

        var watch = new System.Diagnostics.Stopwatch();

        var array = new List<int>();

        var array2 = new List<int>();

        for (int i = 0; i < 1000000; i++)

        {

            array.Add(i);

            array2.Add(i);

        }

        IEnumerable<int> enumerable = array.Select(item => array[item] + array2[item]);

        UseEnumerable(enumerable);

        UseList(enumerable.ToList());

    }

}