using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var badWords = new [] { "butt", "fuck" }; //parametrized in real application

        var badWordsRegex = string.Join("|", badWords);

        var inputTexts = new[]

                {

                    new {input = "fuck", expected = "***"},

                    new {input = "Fuck", expected = "***"},

                    new {input = "butt", expected = "***"},

                    new {input = "something fuck", expected = "something ***"},

                    new {input = "fuck something", expected = "*** something"},

                    new {input = "Something fucker", expected = "Something fucker"},

                    new {input = "Something fuck something", expected = "Something *** something"},

                    new {input = "butter", expected = "butter"},

                    new {input = "butter butt butter", expected = "butter *** butter"},

                    new {input = "XXXbutt butt XXXbutt", expected = "XXXbutt *** XXXbutt"},

                    new {input = "butter butt.butter", expected = "butter ***.butter"},

                    new {input = "butter,butt butter", expected = "butter,*** butter"}

                };

        foreach(var inputText in inputTexts) {

            var cleanedText = Regex.Replace(inputText.input, @"\b(" + badWordsRegex + @")\b", 

                                 delegate(Match m)

                                 {

                                     return "***";

                                 }, RegexOptions.IgnoreCase);

            if(cleanedText == inputText.expected) {

                Console.WriteLine("[{0}] => [{1}]", inputText.input, cleanedText);

            }

            else {

                Console.WriteLine("[{0}] => [{1}] ERROR expected: [{2}]", inputText.input, cleanedText, inputText.expected);

            }

        }

    }

}