using System;

using System.Collections.Generic;

using System.Linq;

​

public static class StringExtensions

{

    public static IEnumerable<string> SplitInParts(this string s, int partLength)

    {

        if (s == null) throw new ArgumentNullException("s");

        if (partLength <= 0) throw new ArgumentException("Part length has to be positive.", "partLength");

        var charCount = 0;

        return s.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).GroupBy(w => (charCount += w.Length + 1) / partLength).Select(g => string.Join(" ", g));

    }

}

​

public class Program

{

    public static void Main()

    {

        string input = "This is a very long string that will be split into many parts because its lenght exceed a certain amount of characters!";       

        var parts = input.SplitInParts(50);

        foreach(var part in parts)

        {

            Console.WriteLine(part);    

        }

    }

}