ASP: ISBN Conversion

Introduction

This code shows examples on how to convert an ISBN10 number to the new ISBN13 number. It also show how to convert ISBN13 to ISBN10, but take in account that this only works for those ISBN13 numbers starting with 978. All other ISBN13'a can't be converted to ISBN10 values.

The following example shows a few example codes on how to implement both ISBN conversions on your site. This code can be useful for those who have an ISBN search or wish to show both ISBN values on their site while only storing one in the database. Important to take in account when working with ISBN's is that the last digit of both ISBN10 and ISBN13 are a control digit that needs to be calculated. We won't go into details of the formula, but one should consider this in any ISBN search system. Some publisher have the wrong ISBN (last digit) listed in their book. In order to offer the best chance of a user finding a book only the first 9 (ISBN10) or 12 (ISBN13) digits should be used in an ISBN search. If you take this into account and the fact the first 9 digits of ISBN10 are equal to digit 4-12 of ISBN13 are equal any conversion not taking the last digit into account for use in a search is very straightforward. In the conversion examples will include a last digit calculator. As last we include a demo and as download an example of ISBN10 or ISBN13 to both ISBN10 and ISBN13 conversion and last digit calculator.

Code

• ASP
• VBScript

<%
' Declare and initialize the variables
Dim strISBN10, strISBN10New
Dim i
Dim intCalc, intCalc2, intCalc3, strCalc4

For i = 1 To 9
	If isNumeric(Mid(strISBN10,i,1)) Then
		intCalc = intCalc + (Mid(strISBN10,i,1) * (11-i))
	End If
Next
intCalc2 = Split((intCalc / 11),".")
intCalc3 = intCalc - (intCalc2(0)*11)
strCalc4 = 11 - intCalc3
If strCalc4 = 10 Then
	strCalc4 = "x"
ElseIf strCalc4 = 11 Then
	strCalc4 = "0"
End If

strISBN10New = Left(strISBN10,9) & strCalc4
%>

You will need to load the strISBN10 variable with the ISBN you want to use to calculate the last digit. The intISBN10New variable will have the result.

<%
' Declare and initialize the variables
Dim intISBN13, intISBN13New
Dim i
Dim intCalc, intCalc2, intCalc3, intCalc4, intMultiply

intMultiply = 1
For i = 1 To 12
	If isNumeric(Mid(intISBN13,i,1)) Then
		intCalc = intCalc + (Mid(intISBN13,i,1) * intMultiply)

		If intMultiply = 1 Then
			intMultiply = 3
		Else
			intMultiply = 1
		End If
	End If
Next
intCalc2 = Split((intCalc / 10),".")
intCalc3 = intCalc - (intCalc2(0)*10)
intCalc4 = 10 - intCalc3
If intCalc4 = 10 Then
	intCalc4 = "0"
End If

intISBN13New = Left(intISBN13,12) & intCalc4
%>

You will need to load the strISBN13 variable with the ISBN you want to use to calculate the last digit. The intISBN13New variable will have the result.

<%
' Declare and initialize the variables
Dim strISBN10, intISBN13, intISBN13New
Dim i
Dim intCalc, intCalc2, intCalc3, intCalc4, intMultiply

intISBN13 = 978 & Left(strISBN10,9)

intMultiply = 1
For i = 1 To 12
	If isNumeric(Mid(intISBN13,i,1)) Then
		intCalc = intCalc + (Mid(intISBN13,i,1) * intMultiply)

		If intMultiply = 1 Then
			intMultiply = 3
		Else
			intMultiply = 1
		End If
	End If
Next
intCalc2 = Split((intCalc / 10),".")
intCalc3 = intCalc - (intCalc2(0)*10)
intCalc4 = 10 - intCalc3
If intCalc4 = 10 Then
	intCalc4 = "0"
End If

intISBN13New = Left(intISBN13,12) & intCalc4
%>

The conversion will add the 978 digits in front of the first 9 digits of the ISBN10. All that remains is calculating the last digit of the ISBN13.

<%
' Declare and initialize the variables
Dim strISBN10, strISBN10New, intISBN13
Dim i
Dim intCalc, intCalc2, intCalc3, strCalc4

If Mid(intISBN13,1,3) = 978 Then
	strISBN10 = Right(Left(intISBN13,12),9)

	For i = 1 To 9
		If isNumeric(Mid(strISBN10,i,1)) Then
			intCalc = intCalc + (Mid(strISBN10,i,1) * (11-i))
		End If
	Next
	intCalc2 = Split((intCalc / 11),".")
	intCalc3 = intCalc - (intCalc2(0)*11)
	strCalc4 = 11 - intCalc3
	If strCalc4 = 10 Then
		strCalc4 = "x"
	ElseIf strCalc4 = 11 Then
		strCalc4 = "0"
	End If

	strISBN10New = Left(strISBN10,9) & strCalc4
End If
%>

This conversion will convert ISBN10 compatible ISBN13 values to ISBN10. If the ISBN13 is not ISBN10 compatible (ie doesn't start with 978) nothing is done. You can add an Else statement to the If Mid(intISBN13,1,3) = 978 statement if you wish to do something when the entered ISBN13 is not ISBN10 compatible.

The following example offers conversion from ISBN10 to ISBN13 as well as ISBN13 to ISBN10, it also checks if the entered ISBN is valid. The complete code is available for download. This code uses the examples shown above in a modified form.

Example: See it in action

Downloads

ASP:
example.zip

<head>
  <title>Flying Lowlander: Code Examples</title>
</head>