using System.Text.RegularExpressions;
public static class HangmanExtensions {
public static string HangmanParse(this string str, string checkLetters) {
if (!string.IsNullOrWhiteSpace(checkLetters)) regexPattern = @"[^" + checkLetters + "]";
return Regex.Replace(str, regexPattern, "_", RegexOptions.IgnoreCase);
public static void Main()
Console.WriteLine(test.HangmanParse("e"));
Console.WriteLine(hero.HangmanParse("hr"));
string thisIsAwesome = "This Is Awesome";
Console.WriteLine(thisIsAwesome.HangmanParse("iwm"));