Regular Expressions Example (c#) – CSharp


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

csc /r:System.Text.RegularExpressions.dll,System.dll Validation.cs
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:”);
Console.WriteLine(“{0} is Valid Alpha String”,strToTest);
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) &&
// 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 +”)|(” +
trValidIntegerPattern + “)”);
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.


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