大佬看一下为啥不能输出答案，还有那个 parseFloa什么意思啊？
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var a = document.getElementById("txt1").value;
var b = document.getElementById("txt2").value;
var c = document.getElementById("select").value;
var result ;
switch(c) {
case "+":
result = parseFloat(a) + parseFloat(b);
break;
case "-":
result = parseFloat(a) - parseFloat(b);
break;
case "*":
result = parseFloat(a) * parseFloat(b);
break;
default:
result = parseFloat(a) / parseFloat(b);
}
document.getElementById("fruit").value = result;
}
</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=' = ' /> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit' />
</body>
</html>
