Hot to add unchecked checkbbox value to array? [duplicate]

This question already has an answer here:

• Get $_POST from multiple checkboxes 5 answers

When press button i want to get array Array ( [0] => 1 [1] => 0 [2] => 1 [3] => 0 )

How can i do that ?

<form id="fid" name="f1" method="post">
    <input name="aa[]" type="checkbox" value="1" checked/>
    <input name="aa[]" type="checkbox" value="1"/>
    <input name="aa[]" type="checkbox" value="1" checked/>
    <input name="aa[]" type="checkbox" value="1" />
    <input type="submit" name="submit" value="Submit" />
</form>