小型计算器-2019年5月10日21点30分

下面将展示小型计算器代码及效果图：
实例

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>迷你计算器</title>
    <style type="text/css">
        .box {
            width: 500px;
            height: 200px;
            background-color: #efefef;
            border: 1px solid lightgray;
            text-align: center;
            margin: 20px auto;
            color: #636363;
            border-radius: 15px;
            box-shadow: 2px 2px 2px #999;
        }

        table {
            margin: auto;
            /*参考线*/
            /*border: 1px solid red; */
        }

        td {
            width: 100px;
            height: 30px;
            padding: 5px 10px;
        }

        input, select {
            width: 100%;
            height:100%;
            border:none;
            text-align: left;
            padding-left: 15px;
            /*background-color: cyan;*/
        }

        button {
            width: 100%;
            height: 100%;
            border: none;
            background-color: skyblue;
            color: white;
        }
        button:hover {
            cursor: pointer;
            background-color: coral;
            width: 105%;
            height: 105%;
        }

    </style>
</head>
<body>
<div class="box">
    <h2>小小计算器</h2>
    <form>
        <table>
            <tr>
                <td><input type="text" name="opt1" placeholder="操作数1" autofocus></td>
                <td>
                    <select name="option">
                        <option value="null">请选择操作</option>
                        <option value="add"> + </option>
                        <option value="sub"> - </option>
                        <option value="mul"> * </option>
                        <option value="div"> / </option>
                    </select>
                </td>
                <td><input type="text" name="opt2" placeholder="操作数2"></td>
                <td><button type="button">计算</button></td>
            </tr>
            <tr>
                <td colspan="2" align="right"><h3>结果:</h3></td>
                <td colspan="2" align="left"><h3 id="result"></h3></td>
            </tr>
        </table>
    </form>
</div>
<script>
    var opt1=document.getElementsByName('opt1')[0];
    var opt2=document.getElementsByName('opt2')[0];
    var opt=document.getElementsByName('option')[0];

    var btn=document.getElementsByTagName('button')[0];
    var result=document.getElementById('result');
    btn.onclick=function(){
        var data1=0;
        var data2=0;
        if(opt1.value.length===0){
            alert('操作不能为空');
            opt1.focus();
            return false;
        }else if(isNaN(opt1.value)){
            alert('必须为数字');
            opt1.focus();
            return false;
        }else if(opt2.value.length===0){
            alert('操作不能为空');
            opt2.focus();
            return  false;
        }else if(isNaN(opt2.value)){
            alert('必须为数字');
            opt2.focus();
            return false;
        }else {
            data1=parseFloat(opt1.value);
            data2=parseFloat(opt2.value);
        }
        var option =opt.value;
        var temp=0;
        var flag='';
        switch (option) {
            case 'null':
                alert('请选择操作类型');
                return  false;
            case 'add':
                flag='+';
                temp=data1+data2;
                break;
            case 'sub':
                flag='-';
                temp=data1-data2;
                break;
            case 'mul':
                flag='*';
                temp=data1*data2;
                break;
            case 'div':
                flag='/';
                if(data2===0){
                    alert('除数不能为0，请重新输入');
                    opt2.focus();
                    return false;
                }else {
                    temp = data1 / data2;
                    temp = Math.round(temp * 100) / 100;
                }
                break;

        }
        var str='<span style="color: coral">';
        str+=data1+flag+data2+'='+temp;
        str+='</span>';
        result.innerHTML=str;
    }



</script>

</body>
</html>
运行实例 »
点击 "运行实例" 按钮查看在线实例
2.本次学到了小型计算机中的基本操作
在写之前掌握一些逻辑性
（1）输入框不能为空
（2）输入框只能为数字
（3）加减乘除用switch 在做除的时候保留两位小数用Math.round(temp * 100) / 100; 数字用 parseFloat(opt1.value);
实例

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