.value问题，求详细解答
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var aValue = parseInt(document.getElementById("txt1").value);
var bValue = parseInt(document.getElementById("txt2").value);
var aSelect = document.getElementById("select").value;
var cValue = document.getElementById("fruit"); // var cValue = document.getElementById("fruit").value;
if(aSelect == "+") // if(aSelect == "+")
{ // {
cValue.value = aValue + bValue; // cValue = aValue + bValue;
} // }
else if (aSelect == "-")
{
cValue.value = aValue - bValue;
}
else if(aSelect == "/")
{
cValue.value = aValue / bValue;
}
else
{
cValue.value = aValue * bValue;
}
}
</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>为什么按照注释的写法运行没有效果？.value有什么时候不能加的？
