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Function to Check the Format of a Telephone Number Format

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People have different thoughts on how they should enter a telephone number into a field on a web form. Some people may enter the number as (nnn) nnn-nnnn and some as nnn-nnn-nnnn and some may omit the area code entirely. Since database formats need to be consistent and field sizes should be kept to a minimum, I found it necessary to write a function to validate telephone number fields before posting them to a database. I prefer the nnn-nnn-nnnn format so that is what I used with this example. This VBScript example accepts a string as the input parameter and returns the Boolean value of True or False.

Private Function ChkPhoneNum(ByVal strPhoneNumber As String) As Boolean
' Check if there are 12 characters in the string
 If strPhoneNumber.Length <> 12 Then
   Return False
 End If

' Turn the sting that was passed into an array
 Dim aPhoneNumber() As String = strPhoneNumber.Split("-")

' Now check if there are three strings in the array
 If aPhoneNumber.Length <> 3 Then
   aPhoneNumber = Nothing
   Return False
 End If

' Now we see if the three individual strings are numbers
 For i As Integer = 0 To 2
   If Not IsNumeric(aPhoneNumber(i)) Then
     aPhoneNumber = Nothing
     Return False
   End If
 Next i

' Now we make sure the individual strings are the correct length
 If (aPhoneNumber(0).Length <> 3) Or _
  (aPhoneNumber(1).Length <> 3) Or _
   (aPhoneNumber(2).Length <> 4) Then
     aPhoneNumber = Nothing
     Return False
 End If

' If we got here then the string is in the correct format
 aPhoneNumber = Nothing
 Return True
End Function

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