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<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>计算器</title>
</head>
<style>
.box{
width:500px;
border:1px solid #ccc;
margin:20px auto;
text-align:center;
border-radius:5px;
box-shadow:2px 2px 2px #ccc;
background-color:#eee;
}
table{
margin:auto;
}
table tr td{
height:30px;
}
input{
width:100px;
}
button{
width:50px;
height:20px;
border:none;
background:lightgreen;
border-radius:5px;
}
button:hover{
cursor:pointer;
background-color:coral;
}
</style>
<body>
<div class="box">
<form>
<table>
<caption>我的计算器</caption>
<tr>
<td><input type="text" placeholder="数字1" name="num1"></td>
<td>
<select>
<option value="null">请选择</option>
<option value="add">+</option>
<option value="sub">-</option>
<option value="mul">*</option>
<option value="div">/</option>
</select>
</td>
<td><input type="text" placeholder="数字2" name="num2"></td>
<td><button type="button">计算</button></td>
</tr>
<tr>
<td colspan="4" id="result">结果 </td>
</tr>
</table>
</form>
</div>
<script>
let num1 = document.getElementsByName('num1')[0];
let num2 = document.getElementsByName('num2')[0];
let type = document.getElementsByTagName('select')[0];
let btn = document.getElementsByTagName('button')[0];
let result = document.getElementById('result');
btn.onclick=function(){
let data1 = 0;
let data2 = 0;
if(num1.value.length === 0){ //判断第一个数字不能为空
alert('数字1 不能为空');
num1.focus();
return false;
}else if(isNaN(num1.value)){ //判断是否为数字
alert('数字1 必须是数字');
num1.focus();
return false;
}else if(num2.value.length === 0){
alert('数字2 不能为空');
num2.focus();
return false;
}else if (isNaN(num2.value)){
alert('数字2 必须是数字');
num2.focus();
return false;
}else{
data1 = parseFloat(num1.value); //parseFloat() 函数可解析一个字符串，并返回一个浮点数。
data2 = parseFloat(num2.value);
}
let option = type.value;
let flag = '';
let temp = 0;
switch(option){
case 'null':
alert('请选择运算符');
return false;
break;
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('第二个除数不能为0');
num2.value = '';
num2.focus();
return false;
}else{
temp = data1 / data2;
temp = Math.round(temp*100)/100; //四舍五入结果保留两位小数
}
break;
}
result.innerHTML = '<span style="color:orange;font-size:16px;">' + data1 + flag + data2 + '=' + temp + '</span>';
}
</script>
</body>
</html>点击 "运行实例" 按钮查看在线实例
