using System;
using System.Text.RegularExpressions;

public class Example
{
   public static void Main()
   {
      String[] expressions = { "16 + 21", "31 * 3", "28 / 3",
                               "42 - 18", "12 * 7",
                               "2, 4, 6, 8" };
      String pattern = @"(\d+)\s+([-+*/])\s+(\d+)";
      foreach (var expression in expressions)
         foreach (Match m in Regex.Matches(expression, pattern)) {
            int value1 = Int32.Parse(m.Groups[1].Value);
            int value2 = Int32.Parse(m.Groups[3].Value);
            switch (m.Groups[2].Value)
            {
               case "+":
                  Console.WriteLine("{0} = {1}", m.Value, value1 + value2);
                  break;
               case "-":
                  Console.WriteLine("{0} = {1}", m.Value, value1 - value2);
                  break;
               case "*":
                  Console.WriteLine("{0} = {1}", m.Value, value1 * value2);
                  break;
               case "/":
                  Console.WriteLine("{0} = {1:N2}", m.Value, value1 / value2);
                  break;
            }
         }
   }
}
// The example displays the following output:
//       16 + 21 = 37
//       31 * 3 = 93
//       28 / 3 = 9.33
//       42 - 18 = 24
//       12 * 7 = 84

using System;
using System.Text.RegularExpressions;

public class Example
{
   public static void Main()
   {
      String input = "[This is captured\ntext.]\n\n[\n" +
                     "[This is more captured text.]\n]\n" +
                     "[Some more captured text:\n   Option1" +
                     "\n   Option2][Terse text.]";
      String pattern = @"\[([^\[\]]+)\]";
      int ctr = 0;
      foreach (Match m in Regex.Matches(input, pattern))
         Console.WriteLine("{0}: {1}", ++ctr, m.Groups[1].Value);
   }
}
// The example displays the following output:
//       1: This is captured
//       text.
//       2: This is more captured text.
//       3: Some more captured text:
//          Option1
//          Option2
//       4: Terse text.

using System;
using System.Collections.Generic;

public class Example
{
   public static void Main()
   {
      String value = "This is the first sentence in a string. " +
                     "More sentences will follow. For example, " +
                     "this is the third sentence. This is the " +
                     "fourth. And this is the fifth and final " +
                     "sentence.";
      var sentences = new List<String>();
      int position = 0;
      int start = 0;
      // Extract sentences from the string.
      do {
         position = value.IndexOf(‘.‘, start);
         if (position >= 0) {
            sentences.Add(value.Substring(start, position - start + 1).Trim());
            start = position + 1;
         }
      } while (position > 0);

      // Display the sentences.
      foreach (var sentence in sentences)
         Console.WriteLine(sentence);
   }
}
// The example displays the following output:
//       This is the first sentence in a string.
//       More sentences will follow.
//       For example, this is the third sentence.
//       This is the fourth.
//       And this is the fifth and final sentence.