Why is this PHP/mYsql not working?

[Mr. Question]

function genRandomString() {
$length = 10;
$characters = "0123456789abcdefghijklmnopqrstuvwxyz";


for ($p = 0; $p < $length; $p++) {
$string .= $characters[mt_rand(0, strlen($characters))];
}

return $string;
}
genRandomString();

mysql_select_db("DATABASE", $con);
$sql = "INSERT INTO hits VALUES ('3', " . $string . ")";
mysql_query($sql);


/////////////////some variables are defined elsewhere