Try to use function argument in PHP to plus and minus int.

**My functions is :**

```
function int_test($arg) {
    $main = date('m');
    return intval($main.$arg);
}

```

**so when i test :**

```
echo int_test(); // 11
echo int_test(-1); // 11
echo int_test(1); // 11

```

Whats happen ? or how can I do ?