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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<h2>计算器</h2>
<div>
<input type="text">
<select id="option" >
<option value="a">+</option>
<option value="b">-</option>
<option value="c">*</option>
<option value="d">/</option>
</select>
<input type="text">
<button>计算器</button>
<hr>
<li></li>
</div>
<script>
var a1 = document.getElementsByTagName("input")[0];
var a2 = document.getElementsByTagName("input")[1];
var opt = document.getElementById("option");
for (i=0; i<opt.length; i++);
var button = document.getElementsByTagName("button")[0];
button.onclick =function () {
var data=0;
var data1=0;
if(a1.value.length===0 && a2.value.length===0){
alert('不能为空');
a1.focus();
a2.foucs();
return false;
}else if ((isNaN(a1.value)) && (isNaN(a2.value))) {
alert('只能为数字');
a1.focus();
a2.foucs();
return false;
}else {
//转换数值
data =parseFloat(a1.value);
data1=parseFloat(a2.value);
}
var opction =opt.value;
var zan=0;
var falg ='';
switch (opction) {
case 'a':
falg ='+';
zan=data + data1;
break;
case 'b':
falg ='-';
zan=data - data1;
break;
case 'c':
falg ='*';
zan=data * data1;
break;
case 'd':
falg ='/';
if(data1 ===0){
alert('除数不能为0');
return falg;
}else{
zan=data / data1;
zan =Math.round(zan *100) /100;
}
break;
}
var li =document.getElementsByTagName("li")[0];
var p =document.createElement("p");
p.innerText= data1 + falg +data1 + '=' + zan ;
li.appendChild(p);
}
</script>
</body>
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