how to post indeterminate checkbox with php?

I have 2 checkboxes. checkbox1 is checked and checkbox2 is indeterminated.

<input type="checkbox" name="checkboxes[]">
<input type="checkbox" name="checkboxes[]">

then i post them to another php. i give them by this code:

foreach($_POST['checkboxes'] as $checkbox){
echo $checkbox;
}

but this code just give checkbox that is checked!