Updating database from an array of input in PHP

  $patient_number = $_GET['patient_number'];
    $quer="SELECT * FROM prescription WHERE patient_number='$patient_number'";
    $resul=mysqli_query($connect,$quer);
    while ($ro=mysqli_fetch_array($resul)){
        $medicine_name = $ro['medicine_name'];
        $query = "UPDATE medicine SET quantity=$quantity WHERE medicine_name ='$medicine_name'";//line 28
        $res = mysqli_query($connect,$query);
    }

The error Warning: Array to string conversion in C:wamp64wwwHMSpharmacyaction.php on line 28 whenever I run my codes