Form-SumTwoNumbers

<?php  declare(strict_types=1) ?>
    <form>
        Number1: <input type="number" value="0" name="num1"/> </br>
        Number2: <input type="number" value="0" name="num2"/> </br>
        <input type="submit" value="Sum" name="sum-btn" />
    </form>
<?php
function sum(int $a, int $b): int {
    return $a + $b;
}

if (isset($_GET['sum-btn'])) {
    $a = intval($_GET['num1']);
    $b = intval($_GET['num2']);
    echo sum($a, $b);
}