有人能帮忙看下是哪里出问题了么运行不出结果
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var a;
var txt1=document.getElementById("txt1").value;
var txt2=document.getElementById("txt2").value;
var txt3=document.getElementById("txt3").value;
switch(txt3){
case "+"
a=parseInt(txt1)+parseInt(txt2);
break
case "-"
a=parseInt(txt1)-parseInt(txt2);
break
case "*"
a=parseInt(txt1)*parseInt(txt2);
break
case "/"
a=parseInt(txt1)/parseInt(txt2);
break
}
document.getElementById('fruit').value=a;
}
</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>
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