using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string test = "a b cdf 7654321";

        string stringBefore = test.Substring(0, test.Length - 7);       

        string integer = test.Substring(test.Length - 7);

        Console.WriteLine("Substring way: ");

        Console.WriteLine("'{0}'", stringBefore);

        Console.WriteLine("'{0}'", integer);

        Console.WriteLine("LINQ Extension method way: ");

        foreach(var s in test.SplitString(7))

        {

            Console.WriteLine("'{0}'", s);

        }

    }

​

}

​

public static class StringExtensions

{

    public static string[] SplitString(this string input, int index)

    {

        if(index < 0 || input.Length < index)

            throw new IndexOutOfRangeException();

        return new string[] 

        {

            String.Concat(input.Take(input.Length - index)),

            String.Concat(input.Skip(input.Length - index))

        };      

    }

}