Why does this code trigger an error?

A PDO object called $db has been set up to use for database operations, including user authentication. All user-related properties are set. The script line public function __construct(&$db) shows a constructor that initializes all user-related properties to _ if no user has logged in. These parameters will be properly set by the login functions when a user logs in.

Assuming that $first_name and $family_name are valid strings, which statement is invalid?

When it comes to the value of a variable, what is the difference between NULL and empty?

If you want to pass a formfield to another page when a button is clicked, you should use the ** . If you want to store information across multiple pages, you should use the ** ?

You are using the following code to decide if a button is clicked, but it is never returning true. Which step is most likely to shed light on the problem? isset($_POST['submit'])

What is a collection of characters that is treated as one entity called?

Which is NOT a function of PHP session support?

Which keyword precedes a method name?

What's the output?

What is the GD Library?