Просмотр поста

<?php

$result = 0;
$operation = ['+', '-', '*', '/'];

$a = filter_input(INPUT_POST, 'a', FILTER_SANITIZE_NUMBER_INT);
$b = filter_input(INPUT_POST, 'b', FILTER_SANITIZE_NUMBER_INT);
$action = filter_input(INPUT_POST, 'action');

if (in_array($action, $operation)) {
    $create = create_function('$a, $b', 'return $a '. $action .' $b;');
    $result = $create($a, $b);
}

?>

<form method="post">
    <input type="text" name="a" />
    <input type="text" name="b" /><br />
    <?php foreach ($operation as $opt) { ?>
        <input type="checkbox" name="action" value="<?php echo $opt; ?>" />
        <?php echo $opt; ?><br />
    <?php } ?>
    <input type="submit" value="Выполнить" />
</form>
<?php echo $result; ?>