Postcode validation VBA

' Validates the postcode entered - Format Check
Private Function validPostcode(postCode) ' Format check
Dim valid As Boolean
Dim first As String
Dim number As String
Dim last As String
Dim poCode As String
Dim space As String
Dim i As String
Dim cha As String
' Splits the postcode into sections.
poCode = tbpostcode.Text
first = Left(poCode, 1)
number = Mid(poCode, 2, 2)
space = Mid(poCode, 4, 1)
last = Right(poCode, 3)
valid = True
' If there is data
If Not poCode = "" Then
valid = True
End If
' Checking the value of first digit
If Not frontLetter(first) Then
valid = False
End If
' Checking the second and third characters
If Not isNumeric(number) <> 7 Then
valid = False
End If
' Checks to see if there is a space
' After the fourth digit
If Not space = "" Then
valid = False
End If
' Checks that last three digits
If Not lastThree(last) Then
valid = False
End If
validPostcode = valid
' Display error if invalid postcode
If valid = False Then
MsgBox "Please enter a valid postcode", vbOKOnly
End If
End Function
 
' Function to validate the front letter of the postcode
Private Function frontLetter(s As String)
Dim ing As Integer
Dim ch As String
Dim valid As Boolean
valid = True
For ing = 1 To Len(s)
ch = Mid(s, ing, 1)
If ch < "A" Or ch > "Z" Then
valid = False
End If
Next ing
frontLetter = valid
End Function
 
' Function to validate numeric value of
' The postcode
Private Function isNumeric(s As String)
Dim ing As Integer
Dim ch As String
Dim valid As Boolean
valid = True
For ing = 1 To Len(s)
ch = Mid(s, ing, 1)
If ch < "0" Or ch > "9" Then
valid = False
End If
Next ing
isNumeric = valid
End Function
 
' Validate last three characters of postcode
Private Function lastThree(s As String)
Dim ing As Integer
Dim ch As String
Dim valid As Boolean
valid = True
For ing = 1 To Len(s)
ch = Mid(s, ing, 1)
If ch < "A" Or ch > "Z" Then
valid = False
End If
Next ing
lastThree = valid
End Function