UPS跟踪号校验代码

每个快递公司生成的单号大部分带自校验功能。下面的代码实现对UPS单号的正确性校验

function validUPS($tr){
$tr = strtoupper(trim($tr));
if (strlen($tr) == 11)
{
$checknumber = 100 - (substr($tr,1, 1) + substr($tr,3, 1) + substr($tr,5, 1) + substr($tr,7, 1) + substr($tr,9, 1) + 2 * (substr($tr,2, 1) + substr($tr,4, 1) + substr($tr,6, 1) + substr($tr,8, 1)));
if ($checknumber = 10)
{
$checknumber = substr($checknumber,1,1);
}
else if ($checknumber = 65 && $i = 73 && $i = 83 && $i = 10)
{
$checknumber = substr($checknumber,1,1);
}
$r= $checknumber == substr($tr,15, 1);
}else {
$r=false;
}
return $r;
}

关键字：php, substr, chr, else