PHP - Handling HTML checkbox array [duplicate]

This question already has an answer here:

• Get $_POST from multiple checkboxes 6 answers

I have a form that has 5 checkboxes. When I submit the form and I print the value of the checkbox array I get the word on for each checkbox that was selected instead of the value.

Here is my HTML

<div class="checkbox">
  <label style="width:auto !important;">
    <input type="checkbox" name="additional[]" value="contact">
    Contact Form
  </label>
</div>
<div class="checkbox">
  <label style="width:auto !important;">
    <input type="checkbox" name="additional[]" value="google">
    Google Map
  </label>
</div>
<div class="checkbox">
  <label style="width:auto !important;">
    <input type="checkbox" name="additional[]" value="sub">
    Subscribe Feature
  </label>
</div>
<div class="checkbox">
  <label style="width:auto !important;">
    <input type="checkbox" name="additional[]" value="caro">
    Image carousel
  </label>
</div>
<div class="checkbox">
  <label style="width:auto !important;">
    <input type="checkbox" name="additional[]" value="bar">
    Search Bar
  </label>
</div>

This is my PHP to get the value of additional[] when the form is submitted,

$add = $_POST["additional"];

I then loop through them to see each checkbox that was selected,

$addThings = "";

foreach($add as $value) {
$addThings.= " $value ";
}
echo $addThings;

The output is this,

on on on

It displays an on for each checkbox that has been selected.

How can I get it to display the actual value?