请检查，谢谢

来源：4-8 编程练习

鲨鱼没有鲨鱼线

2019-11-18 21:33:47

<!DOCTYPE html>
<html>
<head>
    <title> 简易计算器</title>
</head>
<body>
    <input type='text' id='num1' />
    <select id='operate'>
        <option value='+'>+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
    </select>

    <input type='text' id='num2' />
    <input type='button' value=' = ' onclick="count()" />
    <input type='text' id='result' />

    <script type="text/javascript">
        function count() {
            /*此处写代码*/
            var num1 = document.getElementById("num1").value,
                num2 = document.getElementById("num2").value,
                operate = document.getElementById("operate"),
                result = document.getElementById("result");
            function add(num1,num2) {
                return +num1 + +num2;
            }                
            function subtract(num1,num2) {
                return num1-num2;
            }
            function multiply(num1,num2) {
                return num1*num2;
            }
            function divide(num1,num2) {
                return num1/num2;
            }
            operate.onchange = function () {
                switch (operate.value) {
                    case "+":
                        return add(num1,num2);
                        break;
                    case "-":
                        return subtract(num1,num2);
                        break;
                    case "*":
                        return multiply(num1,num2);
                        break;
                    case "/":
                        return divide(num1,num2);
                        break;
                    default:
                        break;
                }
            }
            result.value = operate.onchange();
        }
    </script>
</body>
</html>

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