Hello all! I have an array and variable. If the variable does not exist in the array to be added, if there is - remove from the array. Why not work?

$ar = ["a","b","c"];
$vr = "b";

foreach ($ar as $i => $value) {
    if ($value == $vr) {
        unset ($ar[$i]);
    } else {
        $ar[] = $vr;
        $ar = array_unique($ar);
    }   
}

Thanks.