Различные вопросы по PHP и MySQL

<?php

function parser($str) {
    preg_match('#(.*)(\+|\-|\*|\/)(.*)#', $str, $matches);

    return array($matches[1], $matches[3], str_replace(array('+', '-', '*', '/'), array('plus', 'minus', 'multi', 'divide'), $matches[2]));
}

function proc($args) {
    return $args[2]($args[0], $args[1]);
}

function plus($a, $b) {
    return $a + $b;
}

function minus($a, $b) {
    return $a - $b;
}

function multi($a, $b) {
    return $a * $b;
}

function divide($a, $b) {
    return $b > 0 ? ($a / $b) : 'division by zero';
}

$args = parser('1 + 3');
echo proc($args);

<?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; ?>