Regular Expressions in C#

by Joe on Jul 18th in C#, Regular expressions

I needed to validate a form for numeric and integer fields. The C-Sharp Corner seems to cover Regular Expressions pretty well in this article.

Essentially, I created a new class named RegularExpressions and added the following:

using System.Text.RegularExpressions;

// 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) &&
// 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) &&
// 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) &&
// 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);

Instantiate the class in the form with the textboxes, and there you have it.

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