关于用switch写四则运算

<script>
        var num1 = parseFloat(prompt('请输入第一个数'));
        var num2 = parseFloat(prompt('请输入第二个数'));
        var fuhao = prompt('请输入运算符号');
        switch (fuhao) {
            case "+":
                //var sum = num1+num2;
                alert('两数的运算结果是' + num1 + fuhao + num2 + '=' + (num1 + num2));
                break;
            case "-":
                alert('两数的运算结果是' + num1 + fuhao + num2 + '=' + num1 - num2);
                break;
            case "*":
                alert('两数的运算结果是' + num1 + fuhao + num2 + '=' + (num1 * num2));
                break;
            case "/":
                alert('两数的运算结果是' + num1 + fuhao + num2 + '=' + (num1 / num2));
                break;
            default:
                alert('你输入的运算符号有误');
                break;
        }
    </script>