哪位大佬帮我看看哪出错了？没有输出
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var num1 = document.getElementById("text1").value; //获取第一个输入框的值
var num2 =document.getElementById("text2").value; //获取第二个输入框的值
var algorithm = document.getElementById("select").value; //获取选择框的值
var add;
switch(algorithm){
case "+":add = parseInt(num1)+parseInt(num2);
break;
case "-":add = num1-parseFloat(num2);
break;
case "*":add = parseFloat(num1)*parseFloat(num2);
break;
case "0"：alert("除数不能为零");
break;
default: add = parseFloat(num1)/parseFloat(num2);
break;
} //获取通过下拉框来选择的值来改变加减乘除的运算法则
document.getElementById("fruit").value = add; //设置结果输入框的值
}
</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>
