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                        /JavaScript進階篇

大家看看我的代碼哪有問題，結果總出不來

<!DOCTYPE?html>
<html>
?<head>
??<meta?charset="utf-8">
??<title>事件</title>??
??<script?type="text/javascript">
???function?count()
???{
????var?v1=parselnt(document.getElementById("txt1").value);??//獲取第一個輸入框的值
????var?v2=parselnt(document.getElementById('txt2').value);?//獲取第二個輸入框的值
????var?s1=document.getElementById('select').value;?//獲取選擇框的值
????var?d=0;
????switch('s1')??
????{
????????case?'+'?????????????????????????//獲取通過下拉框來選擇的值來改變加減乘除的運算法則
????????d=parselnt(v1)+parselnt(v2);
????????break;
????????case?'-'
????????d=parselnt(v1)-v2;
????????break;
????????
????????case?'*'
????????d=v1*v2;
????????break;
????????
????????case?'/'
????????d=v1/v2;
????????break;
????????default:
????????alert('代碼錯誤');
????}?
??document.getElementById('fruit').value=d;?//設置結果輸入框的值?????
???}
??</script>?
?</head>?
?<body>
???<input?type='text'?id='txt1'?/>?
???<br>
???<select?id='select'>
??<option?value='+'>+</option>
??<option?value="-">-</option>
??<option?value="*">*</option>
??<option?value="/">/</option>
???</select>
???<br>
???<input?type='text'?id='txt2'?/>?
???<br>
???<input?type='button'?value='?=?'?onclick="count()">?<!--通過?=?按鈕來調用創建的函數，得到結果-->?
???<input?type='text'?id='fruit'?/>???
?</body>
</html>