php文章tag标签的增删

<?phpsession_start(); if($_POST){         $_SESSION['old']=array('one','two','three','four','five');    $_SESSION['old']=array();    $_SESSION['old']=array('two','five');     $new=(array) $_POST['big'];    foreach($new as $k=>$v){        if(!in_array($v,$_SESSION['old'])){            $_SESSION['old'][]=$v;            echo 'add '.$v;            echo '<br />';        }else{            echo 'mod '.$v;            echo '<br />';        }    }    foreach($_SESSION['old'] as $k=>$v){        if(!in_array($v,$new)){            $id=array_keys($_SESSION['old'],$v);            unset($_SESSION['old'][$id[0]]);            echo 'del '.$v;            echo '<br />';        }    }    echo "<pre>";    print_r($_SESSION['old']);}?> <form method="post"> <input type="checkbox" name="big[]" value="one" /> one<br /><input type="checkbox" name="big[]" value="two" /> two<br /><input type="checkbox" name="big[]" value="three" /> three<br /><input type="checkbox" name="big[]" value="four" /> four<br /><input type="checkbox" name="big[]" value="five" /> five<br /><input type="submit" value="submit" name='abc'></form>