Task 37

<?php

function getIssuer($number){
$s = strlen($number);
$prefix1 = substr($number, 0, 1);
$prefix2 = substr($number, 0, 2);
$prefix4 = substr($number, 0, 4);
    if  (($s == 15 && ($prefix2 == 34) || $prefix2 == 37)){
        return('AMEX');
    }
    elseif ($s==16 && $prefix4 == 6011){
        return('Discover');
    }
    elseif ($s==16 && $prefix2>=51 && $prefix2<=55){
        return('Mastercard');
    }
    elseif (($s==16 || $s==13) && $prefix1 == 4){
        return('VISA');
    }
    else {
        return('Unknown');
    }
}