PHP switch计算器

<form action="1.php" method="post">
        <input type="number" name="num1" id="num1">
        <input type="number" name="num2" id="num2">
        <select name="fu">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select>
        <button>提交</button>
    </form>
<?php
if(!empty($_POST['num1'])){
    $num1=floatval($_POST['num1']);
    $num2=floatval($_POST['num2']);
    $fu=$_POST['fu'];  
}
if(!empty($_POST['num1'])){
    switch ($fu) {
        case '+':
        echo $num1+$num2;
        break;
        case '-':
        echo $num1-$num2;
        break;
        case '*':
        echo $num1*$num2;
        break;
        case '/':
        echo $num1/$num2;
        break;
    }
}
?>