Object of class mysqli_result could not be converted to string in

The mysqli_query() method returns an object resource to your $result variable, not a string.

You need to loop it up and then access the records. You just can't directly use it as your $result variable.

while ($row = $result->fetch_assoc()) {
    echo $row['classtype']."<br>";
}

Before using the $result variable, you should use $row = mysqli_fetch_array($result) or mysqli_fetch_assoc() functions.

Like this:

$row = mysqli_fetch_array($result);

and use the $row array as you need.

The query() function returns an object, you'll want fetch a record from what's returned from that function. Look at the examples on this page to learn how to print data from mysql