The following example shows the use of Regular Expresssions in C#.This program has basic validation scripts for validation easily useable in all programs.


/*
<HowToCompile>
  csc /r:System.Text.RegularExpressions.dll,System.dll Validation.cs
</HowToComplie>
*/
  

using System.Text.RegularExpressions;
using System;


class Validation
{
  public static void Main()
  {
    String strToTest;
    Validation objValidate=new Validation();

    Console.Write("Enter a String to Test for Alphabets:");
    strToTest=Console.ReadLine();
    if(objValidate.IsAlpha(strToTest))
    {
      Console.WriteLine("{0} is Valid Alpha String",strToTest);
    }
    else
    {
      Console.WriteLine("{0} is not a Valid Alpha String",strToTest);
    }
  }

  // Function to test for Positive Integers.

  public bool IsNaturalNumber(String strNumber)
  {
    Regex objNotNaturalPattern=new Regex("[^0-9]");
    Regex objNaturalPattern=new Regex("0*[1-9][0-9]*");

    return  !objNotNaturalPattern.IsMatch(strNumber) &&
            objNaturalPattern.IsMatch(strNumber);
  }

  // Function to test for Positive Integers with zero inclusive

    public bool IsWholeNumber(String strNumber)
    {
      Regex objNotWholePattern=new Regex("[^0-9]");

      return !objNotWholePattern.IsMatch(strNumber);
    }

  // Function to Test for Integers both Positive & Negative

    public bool IsInteger(String strNumber)
    {
      Regex objNotIntPattern=new Regex("[^0-9-]");
      Regex objIntPattern=new Regex("^-[0-9]+$|^[0-9]+$");

      return  !objNotIntPattern.IsMatch(strNumber) &&
              objIntPattern.IsMatch(strNumber);
    }

  // Function to Test for Positive Number both Integer & Real

  public bool IsPositiveNumber(String strNumber)
  {
    Regex objNotPositivePattern=new Regex("[^0-9.]");
    Regex objPositivePattern=new Regex("^[.][0-9]+$|[0-9]*[.]*[0-9]+$");
    Regex objTwoDotPattern=new Regex("[0-9]*[.][0-9]*[.][0-9]*");

    return !objNotPositivePattern.IsMatch(strNumber) &&
           objPositivePattern.IsMatch(strNumber)  &&
           !objTwoDotPattern.IsMatch(strNumber);
  }

  // Function to test whether the string is valid number or not
  public bool IsNumber(String strNumber)
  {