How to get the value of unchecked and checked checkboxes

I have a list of checkboxes and want to return their values on submit. I can do this easily for the checked ones, but not for the unchecked? Here's my code so far:

<input type="checkbox" checked="checked" name="addressBooks[]" value="<?php echo $id; ?>">

<?php
if (isset($_POST['submit'])) {
    address_books();
}
function address_books() {
    $book = $_POST['addressBooks'];
    if (!isset($book)) {
        $N = count($book);

        echo("You did not select $N book(s): ");
        for ($i = 0; $i < $N; $i++) {
            echo($book[$i] . " ");
        }
    } else {
        $N = count($book);

        echo("You selected $N book(s): ");
        for ($i = 0; $i < $N; $i++) {
            echo($book[$i] . " ");
        }
    }
}