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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>calculator</title>
<style type="text/css">
.box{
width: 500px;
height: 300px;
background-color: #fefefe;
border: 1px solid grey; /*边框*/
margin:20px auto; /*上下20px*/
text-align: center; /*居中*/
color: #636363;
box-shadow: 2px 2px 2px #999; /*阴影*/
border-radius: 15px; /*圆角*/
}
table{
margin: auto;
}
td {
border: 1px solid grey;
}
input,select {
width: 100%;
height: 100%;
border: none;
}
button{
width: 100%;
height: 100%;
border: none;
}
button:hover {
/*font-size: 1.1em;*/
background-color: coral;
cursor: pointer;
}
</style>
</head>
<body>
<div class="box">
<h1>计算器</h1>
<form >
<table>
<tr>
<td><input type="text" name="c1" placeholder="操作数1"></td>
<td>
<select name="option">
<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" name="c2" placeholder="操作数1"></td>
<td><button type="button">计算</button></td>
</tr>
<tr>
<td colspan="2"><h2>结果</h2></td>
<td colspan="2"><h2 id="placeholder"></h2></td>
</tr>
</table>
</form>
</div>
<script type="text/javascript">
var c1=document.getElementsByName('c1')[0]
var c2=document.getElementsByName('c2')[0]
var c=document.getElementsByName('option')[0]
var btn =document.getElementsByTagName('button')[0]
var placeholder=document.getElementById('placeholder')
btn.onclick =function(){
if (c1.value.lenth==0){
alert('不能为空')
c1.focus()
return false
} else if (isNaN(c1.value)){
alert('非数字')
c1.focus()
} else if (c2.value.lenth==0){
alert('不能为空')
c2.focus()
return false
} else if (isNaN(c2.value)){
alert('非数字')
c2.focus()
} else {
var data1 = parseFloat(c1.value)
var data2 = parseFloat(c2.value)
}
var option =c.value
var temp= 0
var flag =' '
var result = ''
switch (option){
case 'Null':
alert('请选择操作符')
c.foucs()
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='/'
temp= data1/data2
break
}
placeholder.innerHTML = '<span style="color:coral">'+data1+' '+ flag+' '+ data2+' = '+temp +'</span>'
}
// var str = '<span style="color:coral">'
// str += data1+' '+ flag +' '+data2 + ' = ' + temp
// str += '</span>'
// var str=0
placeholder.innerHTML = str
</script>
</body>
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