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Calculate an ISBN checksum?

Posted on 1998-12-16
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Last Modified: 2008-03-10
Hello Everyone,

I am trying to automate a few things here at the office for everyone. One of my projects is to create a simple program (very simple) that calculates the checksum or check digit of an ISBN number.

For example:
If you had an ISBN number of 157521030, the checksum would be 4. I've seen examples to verify the checksum, and I've seen the mathmatical equation, but I was wondering if anyone had a simple function or routine that does this? Perhaps a pointer to one that does?

Any help or guidance would be greatly appreciated.

Sincerely,

Sandra Wallace
sandra_wallace@yahoo.com

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Question by:sandra_wallace
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Author Comment

by:sandra_wallace
ID: 1351401
Edited text of question
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LVL 12

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rwilson032697 earned 200 total points
ID: 1351402
This function will calculate the ISBN checksum:

function ISBNCheckDigit(ISBN :string):char;
var
  CheckSum : integer;
  ModValue : Integer;

begin
  CheckSum := 10 * strtoint(ISBN[1]);
  CheckSum := checksum + 9 * strtoint(ISBN[3]);
  CheckSum := checksum + 8 * strtoint(ISBN[4]);
  CheckSum := checksum + 7 * strtoint(ISBN[6]);
  CheckSum := checksum + 6 * strtoint(ISBN[7]);
  CheckSum := checksum + 5 * strtoint(ISBN[8]);
  CheckSum := checksum + 4 * strtoint(ISBN[9]);
  CheckSum := checksum + 3 * strtoint(ISBN[10]);
  CheckSum := checksum + 2 * strtoint(ISBN[11]);
 
  ModValue := Checksum mod 11;
  if ModValue < 10 then
    result := chr(asc('0') + ModValue - 1)
  else
    result := 'X';
end;

Cheers,

Raymond.
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LVL 12

Expert Comment

by:rwilson032697
ID: 1351403
Oops,  this line

 result := chr(asc('0') + ModValue - 1)

should read

 result := chr(ord('0') + ModValue - 1)

Cheers,

Raymond.
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