<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
//获取第一个输入框的值
var num1=document.getElementById('txt1').value;
//获取第二个输入框的值
var num2=document.getElementById('txt2').value;
//获取选择框的值
var select=document.getElementById('select').value;
var sum;
//获取通过下拉框来选择的值来改变加减乘除的运算法则
if(select=='+'){
sum=parseInt(num1)+parseInt(num2);
}else if(select=='-'){
sum=parseInt(num1)-parseInt(num2);
}else if(select=='*'){
sum=parseInt(num1)*parseInt(num2);
}else if(select=='/'){
sum=parseInt(num1)/parseInt(num20;
}else{
document.write("请选择一个");
}
//设置结果输入框的值
document.getElementById('fruit').value=sum;
}
</script>
</head>
<body>
<input type='text' id='txt1' />
<select id='select'>
<option value='+'>+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input type='text' id='txt2' />
<input type='button' value=' = ' onclick="count()"/> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit' />
</body>
</html>
if语句里的else if(select=='/'){
sum=parseInt(num1)/parseInt(num20; 这里0改为’）’估计你打太快了