Check that the ISBN number is legal

[Program Language] Php

[Source Source] Http://px.sklar.com
[Feature description] Check that the ISBN number entered by the user (which can or may not have hyphens) is legal.

The source code is as follows:

/*
* Check to-if the entered ISBN is valid and return
* True or False depending.
* I ' m not even going to try to claim the copyright for such
* A simple thing. Do what are with it.
* 8-) Keith Nunn, kapn@anglican.ca.
*/
function Checkisbn ($ISBN) {
$ISBN = Ereg_replace ("[^0-9x]", "", $ISBN);
$checkdigit = one-((a) substr ($ISBN 10,0,1) + 9 * substr ($ISBN 10,1,1) + 8 * substr ($ISBN 10,2,1) + 7 * substr ($ISBN 10,3 , 1) + 6 * substr ($ISBN 10,4,1) + 5 * substr ($ISBN 10,5,1) + 4 * substr ($ISBN 10,6,1) + 3 * substr ($ISBN 10,7,1) + 2 * SUBSTR ($ isbn10,8,1))% 11);
if ($checkdigit = =) $checkdigit = "X";
if ($checkdigit = one) $checkdigit = 0;
if ($checkdigit = = substr ($isbn 10,9,1)) {
return true;
}
else {
return false;
}
}
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