Code:
<form action="/vote.php" method="post">
    <input type="checkbox" name="answer[]" value="0"> 0<br />
    <input type="checkbox" name="answer[]" value="1"> 1<br />
    <input type="checkbox" name="answer[]" value="2"> 2<br />
    <input type="checkbox" name="answer[]" value="3"> 3<br />
    <input type="hidden" name="addvote" value="1">
    <input type="image" name="vote" alt="Glasaj" value="Glasaj" src="/images/votebutton.gif" width="41" height="22" border="0">
</form>

Code:
if(isset($_POST['answer'])) {
    echo $odgovori = $_POST['answer'];
} else {
    echo 'Nista nije obelezeno';
}
if(is_array($odgovori)) {
    foreach($odgovori as $key=>$value) {
        echo "Checkbox $key: $value";
    }
}