Find a Missing ISBN Number

Category:

Miscellaneous

Type:

Snippets

Difficulty:

Beginning

Author:

Rob S

Version Compatibility: Visual Basic 6

More information:

This snippet will find a missing ISBN number and determine if an ISBN number is valid. The missing character should be replaced with a '?', the ISBN number may only contain characters 0-9, 'X' (the value of 10) and '-'.

Instructions: Copy the declarations and code below and paste directly into your VB project.

Declarations:
'******************************** '* Written By: Rob S * '* Date: Nov 2003 * '* E-Mail: rjs9565@aol.com * '********************************

Code:

'********************************
'*  Written By: Rob S           *
'*        Date: Nov 2003        *
'*      E-Mail: rjs9565@aol.com *
'********************************

'Determines if a given string is a valid ISBN number
Public Function IsISBN(ByVal ISBN As String) As String

'********************************
    '*  Written By: Rob S           *
    '*        Date: Nov 2003        *
    '*      E-Mail: rjs9565@aol.com *
    '********************************

Dim Query As String
    
    Query = Left(ISBN, 1)
    IsISBN = (GetISBNNumber("?" & Right(ISBN, Len(ISBN) - 1)) = Query)

End Function

' Find Missing Number using '?' as the query character
' If ReturnFull = True Then will return entire ISBN including '-'
' Else will return ONLY the missing value
Public Function GetISBNNumber(ByVal ISBN As String, Optional ReturnFull As Boolean = False) As String

'********************************
    '*  Written By: Rob S           *
    '*        Date: Nov 2003        *
    '*      E-Mail: rjs9565@aol.com *
    '********************************

Dim Char(1 To 10) As Variant
    Dim Sum As Long
    Dim x As Long
    Dim xN As Long
    Dim i As Long
    Dim oldISBN As String

' Check ISBN is Valid 10 Digit Number with 1 "?" Query Character
    If Len(ISBN) <> 10 Or CountChar(ISBN, "?") <> 1 Then
        
        If Len(Replace(ISBN, "-", "")) <> 10 Or CountChar(ISBN, "?") <> 1 Then
        
            Exit Function
            
        Else
            
            oldISBN = ISBN
            ISBN = Replace(ISBN, "-", "")
        
        End If
        
    End If
    
    ' Check all "X" Characters are Uppercase
    ISBN = UCase(ISBN)

' Find Number for "?" Character
    For i = 1 To 10
    
        Char(i) = Replace(Right(Left(ISBN, i), 1), "X", "10")
    
        If Char(i) = "?" Then
        
            Char(i) = i & "?"
            x = i
        
        Else
        
            Sum = Sum + (i * Char(i))
            
        End If
        
    Next i
    
    Sum = (Sum Mod 11)
    xN = (11 - Sum) Mod 11
    
    For i = 0 To 10
    
        If (x * i) Mod 11 = xN Then
        
            If ReturnFull = True Then
                GetISBNNumber = Replace(oldISBN, "?", Replace(i, "10", "X"))
            Else
                GetISBNNumber = Replace(i, "10", "X")
            End If
            
            Exit For
            
        End If
        
    Next i

End Function

' Count Occurences of String in Another
Private Function CountChar(ByVal Data As String, ByVal Str As String) As Long

'********************************
    '*  Written By: Rob S           *
    '*        Date: Nov 2003        *
    '*      E-Mail: rjs9565@aol.com *
    '********************************

Dim i As Long
    Dim lSize  As Long
    Dim lCount As Long
    
    lSize = Len(Str)
    
    For i = lSize To Len(Data)
    
        If Right(Left(Data, i), lSize) = Str Then lCount = lCount + 1
    
    Next i

CountChar = lCount

End Function