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                        /JavaScript進(jìn)階篇

我的代碼哪里錯(cuò)了呢

<!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?symbol?=?document.getElementById("select").value;
????var?result="";
????
????switch(symbol)
????case?"+":
????????result?=?parseFloat(a)?+?parseFloat(b);
????????break;
????case?"-":
????????result?=?parseFloat(a)?-?parseFloat(b);
????????break;
????case?"*":
????????result?=?parseFloat(a)?*?parseFloat(b);
????????break;
????case?"/":
????????result?=?parseFloat(a)?/?parseFloat(b);
????????break;
????//設(shè)置結(jié)果輸入框的值?
????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='?=?'?onclick="count()"/>?<!--通過?=?按鈕來調(diào)用創(chuàng)建的函數(shù)，得到結(jié)果-->?
???<input?type='text'?id='fruit'?/>???
?</body>
</html>