How to validate postcode in VB.NET? - vb.net

Question

I'm trying to validate a postcode from a user input within a form. Using this class, i'm trying to search through every character and check it. Then to call in within the form I have used the latter code.
The problem i'm having is that an error pops up saying
"Conversion from string "True0" to type 'Double' is not valid."
Function VaidatePostCode(ByVal Post As String) As String
For C = 0 To Len(Post) - 1
If Char.IsLetter(Post(C)) & C = 0 Then
_boolvalid = True
Else
_boolvalid = False
End If
If Char.IsLetter(Post(C)) & C = 1 Then
_boolvalid = True
Else
_boolvalid = False
End If
If Char.IsNumber(Post(C)) & C = 2 Then
_boolvalid = True
Else
_boolvalid = False
End If
If Char.IsWhiteSpace(Post(C)) & C = 3 Then
_boolvalid = True
Else
_boolvalid = False
End If
If Char.IsNumber(Post(C)) & C = 4 Then
_boolvalid = True
Else
_boolvalid = False
End If
If Char.IsLetter(Post(C)) & C = 5 Then
_boolvalid = True
Else
_boolvalid = False
End If
If Char.IsLetter(Post(C)) & C = 6 Then
_boolvalid = True
Else
_boolvalid = False
End If
Next C
Return _boolvalid
End Function
This is the code within the VB.NET form
Private Sub txtPost_Validated(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtPost.Validated
If myVal.VaidatePostCode(txtPost.Text) = False Then
MsgBox("Please enter correct data format into postcode")
End If
End Sub

Answer 1

To check if the value is a number you can use Integer.TryParse like this:
If Not Integer.TryParse(txtPost.Text, intTemp) Then
MsgBox ...