using System;

using System.Collections.Generic;

using System.Linq;

​

public static class Ext

{

    public static IEnumerable<string> Chunk(this string str, int chunkSize)

    {

        if(chunkSize <= 0)

            throw new ArgumentException("Chunk size cannot be lesser then 0.", nameof(chunkSize));

        return Enumerable

            .Range(0, (int)Math.Ceiling((double)str.Length / chunkSize))

            .Select(i => str.Substring(i * chunkSize, Math.Min(chunkSize, str.Length - (i * chunkSize))));

    }

    public static void ForEach<T>(this IEnumerable<T> collection, Action<T> action)

    {

        if(collection != null && action != null)

        {

            foreach(var item in collection)

                action(item);

        }

    }

    public static string Implode(this IEnumerable<string> collection, string delimiter)

    {

        if(collection == null)

            throw new ArgumentNullException(nameof(collection));

        if(delimiter == null)

            delimiter = "";

        return String.Join(delimiter, collection);

    }

}

public class Program

{

    const string TestString = "1234567890abcdefgh";

    public static void Main()

    {

        TestString.Chunk(4).ForEach(i => Console.WriteLine(i));

        Console.WriteLine();

        Console.WriteLine(TestString.Chunk(5).Implode("-"));

    }

}