AlphabetPosition "The sunset sets at twelve o' clock." => "20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11" as a string

AlphabetPosition.cs

        /// <summary>
        /// Replace every letter with its position in the alphabet.
        /// If anything in the text isn't a letter, ignore it and don't return it.
        /// A being 1, B being 2, etc.
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        public static string AlphabetPosition(string text)
        {
            int index;
            StringBuilder sB = new StringBuilder();

            // Replace everything that is not (^) a word character (\w), a digit (\d) or whitespace (\s) with an empty string.
            string stringWithoutSpecialCharacters = Regex.Replace(text, @"[^\w\d\s]", "");
            foreach (char item in stringWithoutSpecialCharacters)
            {
                index = char.ToUpper(item) - 64;
                if (index > 0 && index <= 30)
                {
                    sB.Append(index);
                    sB.Append(" ");
                }
            }
            return sB.ToString().TrimEnd();
        }

AlphabetPosition2.cs

        /// <summary>
        /// Same as AlphabetPosition, just in one line.
        /// </summary>
        /// <param name="text"></param>
        /// <returns></returns>
        public static string AlphabetPosition2(string text)
        {
            return string.Join(" ", text.ToLower().Where(char.IsLetter).Select(x => x - 'a' + 1));
        }