enumerating-enumerators-enumeratorenumerator.cs

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var lists = new[] { new[] { 1, 2, 3 }.ToList(), new[] { 4, 5, 6 }.ToList() };

        var enumerators = lists.Select(x => x.GetEnumerator()).ToList();

        var enumeratorEnumerator = enumerators.GetEnumerator();

        while(enumeratorEnumerator.MoveNext()) // *******
        {
            ((IEnumerator<int>)enumeratorEnumerator.Current).MoveNext(); // ******
        }

        var values = enumerators.Select(x => x.Current).ToArray();

        Console.WriteLine("{0}, {1}", values[0], values[1]); // Writes 0, 0 (as in, default(int), default(int))
        Console.ReadKey();
    }
}

enumerating-enumerators-for.cs

using System;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var lists = new[] { new[] { 1, 2, 3 }.ToList(), new[] { 4, 5, 6 }.ToList() };

        var enumerators = lists.Select(x => x.GetEnumerator()).ToArray();

        for (int i = 0; i < enumerators.Length; i++ ) // *******
        {
            enumerators[i].MoveNext(); // ******
        }

        var values = enumerators.Select(x => x.Current).ToArray();

        Console.WriteLine("{0}, {1}", values[0], values[1]); // Writes 1, 4
        Console.ReadKey();
    }
}

enumerating-enumerators-foreach.cs

using System;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var lists = new[] { new[] { 1, 2, 3 }.ToList(), new[] { 4, 5, 6 }.ToList() };

        var enumerators = lists.Select(x => x.GetEnumerator()).ToArray();

        foreach (var enumerator in enumerators) // *******
        {
            enumerator.MoveNext(); // ******
        }

        var values = enumerators.Select(x => x.Current).ToArray();

        Console.WriteLine("{0}, {1}", values[0], values[1]); // Writes 0, 0 (as in, default(int), default(int))
        Console.ReadKey();
    }
}

enumerator-foreach-with-print.cs

using System;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var lists = new[] { new[] { 1, 2, 3 }.ToList(), new[] { 4, 5, 6 }.ToList() };

        var enumerators = lists.Select(x => x.GetEnumerator()).ToArray();

        foreach (var enumerator in enumerators) // *******
        {
            enumerator.MoveNext(); // ******
            Console.WriteLine(enumerator.Current); // writes 1, then 4
        }

        var values = enumerators.Select(x => x.Current).ToArray();

        Console.WriteLine("{0}, {1}", values[0], values[1]); // Writes 0, 0 (as in, default(int), default(int))
        Console.ReadKey();
    }
}