Regular expressions in C#

BasicRegex.cs

using System;
using System.Text;
using System.Text.RegularExpressions;

namespace RegularExpressions
{
    class BasicRegex
    {
        static void Main(string[] args)
        {
            string testString = "regular expressions are sometimes called regex or regexp";
            Console.WriteLine("The test string is\n    \"{0}\"", testString);
            Console.Write("Match 'e' in the test string: ");

            // Match 'e' in the test string 
            Regex expression = new Regex("e");
            Console.WriteLine(expression.Match(testString));
            Console.Write("Match every 'e' in the test string: ");

            // match 'e' multiple times in the test string
            foreach (var myMatch in expression.Matches(testString))
                Console.Write("{0} ", myMatch);

            Console.Write("\nMatch \"regex\" in the test string: ");

            // match 'regex' in the test string
            foreach (var myMatch in Regex.Matches(testString, "regex"))
                Console.Write("{0} ", myMatch);

            Console.Write("\nMatch \"regex\" or \"regexp\" using an optional 'p': ");

            // use the ? quantifier to include an optional 'p'
            foreach (var myMatch in Regex.Matches(testString, "regexp?"))
                Console.Write("{0} ", myMatch);

            // use alteration to match either cat or hat
            expression = new Regex("(c|h)at");
            Console.WriteLine("\n\"hat cat\" matches {0}, but \"cat hat\" matches {1}", expression.Match("hat cat"), expression.Match("cat hat"));
        }
    }
}

CharacterClasses.cs

using System;
using System.Text.RegularExpressions;
using System.Text;

namespace CharacterClasses
{
    class CharacterClasses
    {
        static void Main(string[] args)
        {
            string testString = "abc, DEF, 123";
            Console.WriteLine("The test string is: \"{0}\"", testString);

            // find the digits in the test string
            Console.WriteLine("Match any digit");
            DisplayMatches(testString, @"\d");

            // find anything that isn't a digit
            Console.WriteLine("\nMatch any nondigit");
            DisplayMatches(testString, @"\D");
            
            // find the word characters in the test string
            Console.WriteLine("\nMatch any word character");
            DisplayMatches(testString, @"\w");

            // Find sequences of word characters 
            Console.WriteLine("\nMatch a group of at least one word character");
            DisplayMatches(testString, @"\w+");

            // Use a lazy quantifier 
            Console.WriteLine("\nMatch a group of at least one word character (lazy)");
            DisplayMatches(testString, @"\w+?");

            // match characters from a to f
            Console.WriteLine("\nMatch anything from 'a' - 'f'");
            DisplayMatches(testString, "[a-f]");

            // Match anything that isn't in the range 'a' to 'f'
            Console.WriteLine("\nMatch anything not from 'a' - 'f'");
            DisplayMatches(testString, "[^a-f]");

            // Match any sequence of letters in any case
            Console.WriteLine("\nMatch a group of at least one letter");
            DisplayMatches(testString, "[a-zA-Z]+");

            // Use the . (dot) metacharacter to match any character
            Console.WriteLine("\nMatch a group of any characters");
            DisplayMatches(testString, ".*");
        }

        // display the matches to a regular expressions
        private static void DisplayMatches(string input, string expression) 
        {
            foreach (var regexMatch in Regex.Matches(input, expression))
                Console.Write("{0} ", regexMatch);

            Console.WriteLine(); // Move to next line
        }
    }
}