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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>计算器</title>
<style>
body {
background-color: #eee;
}
.box {
margin: 50px 500px;
padding: 10px;
width: 500px;
height: 300px;
background-color: #fff;
box-shadow: 0 0 20px 0 rgb(0,0,0,0.3);
overflow: hidden;
}
.box h2 {
text-align: center;
line-height: 80px;
color: #666;
}
.box input {
padding: 5px 10px;
width: 110px;
margin-right: 2px;
}
.box select {
padding: 5px 10px;
}
.box button {
padding: 4px 8px;
width: 80px;
}
.box .res {
height: 70px;
}
.box .left {
margin-left: 80px;
}
.box .right {
padding: 0 10px;
color: #fb6318;
}
</style>
</head>
<body>
<div class="box">
<h2>计算器</h2>
<form>
<table>
<tbody>
<tr>
<td>
<input type="text" name="opt1" placeholder="操作数1">
</td>
<td>
<select name="option">
<option value="null">请选择操作符</option> <option value="0">请选择操作符</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 class="res" colspan="4">
<span class="left">计算结果：</span>
<span class="right">1</span>
</td>
</tr>
</tbody>
</table>
</form>
</div>
</body>
<script>
// 1.获取操作，按钮，结果占位符的值
let opt1=document.getElementsByName('opt1')[0];
let opt2=document.getElementsByName('opt2')[0];
let opt=document.getElementsByName('option')[0];
let btn=document.getElementsByTagName('button')[0];
let result=document.getElementsByClassName('right')[0];
// 2.给按钮添加事件，进行计算
btn.onclick=function () {
//操作数初始化
let data1 = 0;
let data2 = 0;
if (opt1.value.length === 0) {
alert('第一个操作数不能为空');
opt1.focus();
return false;
} else if (isNaN(opt1.value)) {
alert('第一个操作数必须为数字');
opt1.focus();
return false;
} else if (opt2.value.length === 0) {
alert('第二个操作数不能为空');
opt2.focus();
return false;
} else if (isNaN(opt2.value)) {
alert('第二个操作数必须为数字');
opt2.focus();
return false;
} else {
data1 = parseFloat(opt1.value);
data2 = parseFloat(opt2.value);
}
//对操作符进行处理
let option = opt.value;
let temp = 0;
let flag = '';
switch (option) {
case 'null':
alert('请选择操作类型');
opt.focus();
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 = '/';
//进行除数不能为零的判断和处理
if (data2 === 0) {
alert('除数不能为零');
opt2.focus();
opt2.value = '';
return false;
} else {
temp = data1 / data2;
// 四舍五入保留二位小数
temp = Math.round(temp * 100) / 100;
}
break;
}
let str = '';
str += data1 + ' ' +flag + ' ' + data2 + ' = ' +temp;
result.innerHTML = str;
}
</script>
</html>点击 "运行实例" 按钮查看在线实例
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