Getting the table names

I want to show the table names on my website. At the moment there are two tables stored in my Database.

$sql = "SHOW TABLES";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo $row;
    }
} 
$conn->close();

The output is: ArrayArray

What do I have to do to get the names of the tables?