Where am I wrong?
The code looks OK, but the function returns NULL.
$ar = array(1, 2, 3, 4, 5, 6, 7, 8, 9);
$n = 6;
$new_n = chckn($n, $ar);
echo $new_n;
function chckn($n, $ar) {
    if(!in_array($n, $ar)) {
        echo "===$n===\n";
        return $n;
    } else {
        $n = rand(1, 10);
        chckn($n, $ar);
    }
}
 
     
    