<?php
function randLetter()
{
    $int = rand(0,51);
    $a_z = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $rand_letter = $a_z[$int];
    return $rand_letter;
}
$secretCode = "rTr";

function randChars($num)	{
	$string = "";
	for($i = 0; $i < $num; $i++){
        	$string .= randLetter();
	};
	return $string;
};
$string = $string.randChars(7);
$string = $string.$secretCode;
$string = $string.randChars(10);

echo "code=$string";

?>