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)
{
Regex objNotNumberPattern=new Regex("[^0-9.-]");
Regex objTwoDotPattern=new Regex("[0-9]*[.][0-9]*[.][0-9]*");
Regex objTwoMinusPattern=new Regex("[0-9]*[-][0-9]*[-][0-9]*");
String strValidRealPattern="^([-]|[.]|[-.]|[0-9])[0-9]*[.]*[0-9]+$";
String strValidIntegerPattern="^([-]|[0-9])[0-9]*$";
Regex objNumberPattern =new Regex("(" + strValidRealPattern +")|(" + strValidIntegerPattern + ")");

return !objNotNumberPattern.IsMatch(strNumber) &&
!objTwoDotPattern.IsMatch(strNumber) &&
!objTwoMinusPattern.IsMatch(strNumber) &&
objNumberPattern.IsMatch(strNumber);
}

// Function To test for Alphabets.

public bool IsAlpha(String strToCheck)
{
Regex objAlphaPattern=new Regex("[^a-zA-Z]");

return !objAlphaPattern.IsMatch(strToCheck);
}

// Function to Check for AlphaNumeric.

public bool IsAlphaNumeric(String strToCheck)
{
Regex objAlphaNumericPattern=new Regex("[^a-zA-Z0-9]");

return !objAlphaNumericPattern.IsMatch(strToCheck);
}

}

There is another simple way to perform these validation think of it while the next article comes.