为什么我的得不出结果啊？
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var s1 = parseInt(document.getElementById("txt1").value);
var s3 = parseInt(document.getElementById("txt2").value);
var s2 = document.getElementById("select").value;
var sum = ' ';
switch(s2)
{
case "+";
sum=s1+s2;
break;
case "-";
sum=s1-s2;
break;
case "*";
sum=s1*s2;
break;
case "/";
sum=s1/s2;
break;
}
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>
