检查用户输入的ISBN号码(可以带也可以不带连字符号)是否合法。
源代码如下：
＜?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;}}?＞
