using System;

using System.Collections.Generic;

using System.Text;

​

string value = "This is a test to get the longest word";

static IEnumerable<string> GetWords(string input)

{

    string value = "This is a test to get the longest word";

    // initialize for the first word

    var word = new StringBuilder();

    foreach (var character in input)

    {

        if (char.IsLetter(character))

        {

            word.Append(character);

        }

        else

        {

            if (word.Length > 0)

            {

                yield return word.ToString();

            }

            // reset word

            word = new StringBuilder();

        }

    }

}