PHP koda za izračuna števil

function zracuni($n, $n1,$operation)
{
switch($operation)
{
case '+':$result = $n + $n1; break;
case '-':$result = $n - $n1;break;
case '*':$result = $n * $n1;break;
case '/': $result = $n / $n1;break;
return $result;
}
}

<input type="text" name="prvo" />
<input type="text" name="drugo" />
<input type="submit" value="Izracun" />

<?= (int)$_POST['prvo'] + (int)$_POST['drugo'] ?>