Generate Random String - Fixed !

<?php

function genRandomString($length = 15) {

    $validCharacters = "abcdefghijklmnopqrstuxyvwzABCDEFGHIJKLMNOPQRSTUXYVWZ";
    $validCharNumber = strlen($validCharacters);

    $result = "";

    for ($i = 0; $i < $length; $i++)
    {
        $index = mt_rand(0, $validCharNumber - 1);
            $result .= $validCharacters[$index];
    }

    return $result;

}

$i = 0;

$total = 100;

while($i < $total)
{
    $code = genRandomString();
    $length = strlen($code);

    if($length == 15)
    {
        echo "<span style=\"background-color: green;\">$code - $length chars</span><br/>";
    }
    else
    {
        echo "<span style=\"background-color: red;\">$code - $length chars</span><br/>";
    }

    $i++;
}


?>