检查ISBN号码是否合法

[程序语言] PHP [源码来源] http://px.sklar.com [功能描述] 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. * Im not even going to try to claim copyright for such * a simple thing. Do what you will with it. * 8-) Keith Nunn, [e-mail] */ 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; } } ?＞