Validating the checkbox in PHP

If the checkbox is checked, then the value of checkbox will be passed on the submission of the form. Otherwise, the value is empty. You can validate the value of a checkbox only after the form is being submitted.

For example:

<input type='checkbox' name='accept' value='1' id='checkbox' /> I accept the Terms & Conditions.

Use the following to check/validate the checkbox value at the server end

if (isset($_POST['accept'])) {
    echo "checked!";
}

Or 
if (!empty($_POST['accept'])) {
    echo "checked!";
}

Or 
if(isset($_POST['accept’]) && $_POST[‘accept’]!="")
{
    echo "checked!";
}