PHP function does not return alphanumeric string
<p>I constructed a php function given below to return a string for eg. 007ABX, but function does not return that string..</p>

<pre><code>function abc($aa)
{
    //some code goes here
    $az = range('a', 'z');
$r = array_rand($az, 2);
$str = $az[$r[0]] . $az[$r[1]];
    $new =$aa.$str;

    return $new;
}

$ab = abc($aa);
echo $ab //$ab does not print anything here.
</code></pre>
