I've retried solving this, by using a condition and a default attribute as recommended.

User-generated data is declared before to $Variable\_1:

```
<?php 

$Variable_1 = 'abc123!' //The user inputs the data

if ($booleanvalue == true) { // User selects if they've put data
name($user_data, $Variable_0 = $Variable_1 );
}

//Then the function will use the user's data from $Variable_1

function name($user_data, $Variable_0 = null) {

//Other code...

}

  $Variable_2 = name($user_data);
  $data['variable_2'] = $Variable_2;

?>

```

Is it possible to have $Variable\_0 pre-declared and then put as an argument?