using System;

using System.Collections.Generic;

​

public static class Extension

{

    public static IEnumerable<int> SplitInts(this string source)

    {

        for (var i = 0; i < source.Length; i += 2)

            yield return int.Parse(source.Substring(i, Math.Min(2, source.Length - i)));

    }

}

​

public class Program

{

    public static void Main()

    {

        var test = "23456";

        foreach (var item in test.SplitInts())

            Console.WriteLine(item);

    }

}