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                        /JavaScript進階篇

能幫忙找找問題在哪嗎

<!DOCTYPE?html>
<html>
?<head>
??<title>?事件</title>??
??<script?type="text/javascript">
???function?count(){
???????
????var?a=document.getElementById(txt1).value;//獲取第一個輸入框的值
????var?b=document.getElementById(select).value;//獲取第二個輸入框的值
????var?c=document.getElementById(txt2).value;//獲取選擇框的值
????var?d="";
????switch(b){
?????case?"+":
?????????d=parseInt(a)+parseInt(c);
?????????break;
?????case?"-":
?????????d=a-c;
?????????break;
?????case?"*":
?????????d=a*c;
?????????break;
?????case?"/":
?????????d=a/c;
?????????break;
????}//獲取通過下拉框來選擇的值來改變加減乘除的運算法則
???document.getElementById(fruit).value=d?//設(shè)置結(jié)果輸入框的值?
????
???}
??</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>