＜?php
/*
* Check to see if the entered isbn is valid and return
* true or false depending.
* I'm not even going to try to claim copyright for such
* a simple thing. Do what you will with it.
* 8-) Keith Nunn, kapn@anglican.ca
*/
function checkisbn($isbn) {
$isbn10 = ereg_replace("[^0-9X]","",$isbn);
$checkdigit = 11 - ( ( 10 * substr($isbn10,0,1) + 9 * substr($isbn10,1,1) + 8 * substr($isbn10,2,1) + 7 * substr($isbn10,3,1) + 6 * substr($isbn10,4,1) + 5 * substr($isbn10,5,1) + 4 * substr($isbn10,6,1) + 3 * substr($isbn10,7,1) + 2 * substr($isbn10,8,1) ) % 11);
if ( $checkdigit == 10 ) $checkdigit = "X";
if ( $checkdigit == 11 ) $checkdigit = 0;
if ( $checkdigit == substr($isbn10,9,1) ) {
return true;
}
else {
return false;
}
}
?＞
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