Vaildate Zip Code Using a Regular Expression

Hello, I would like to validate a zip code using a regular expression.  The zip code must be in one of two formats.

The first is:

nnnnn where n is any digit including zero.  5 digits are required (they must all be numbers)

The second is:

nnnnn-nnnn where n is any digit including zero.  this MUST have the hypen between the fifth and seventh character and there must be 5 numercial values to the left of the hypen and four numerical values to the right of the hypen.  

Thanks for your help, sorry I'm bad at these :-)
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GohdanTheMoblinConnect With a Mentor Commented:
Although now that I think about it, you may mean that you aren't sure how to write a function to do it, so I figured while I'm here I'd make it:

    Imports System.Text.RegularExpressions 'add this to the file

    Private Function IsValidZip(ByVal ZipString As String) As Boolean
        Dim pattern As String = "^\d{5}(-\d{4})?$"
        Dim expression As Regex = New Regex(pattern)

        Return expression.IsMatch(ZipString)
    End Function

This function will return true if the argument string is a valid Zip Code, 5-digit or 9-digit.
Hans LangerCommented:
Hi!, Try this,

Digit Zipcode
^\d{5}$ matches 12879, 97211.

^\d{5}-\d{4}$ matches 97211-1234.

You can catch either one with only one expression:
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