                        課程
                    
                        /前端開發
                        
                            /JavaScript
                        
                        /JavaScript進階篇

絕望了，沒有輸出

<!DOCTYPE?html>
<html>
?<head>
??<title>事件</title>??
??<script?type="text/javascript">
???function?count()
???{
????var?num1?=?document.getElementById("txt1").value;????//獲取第一個輸入框的值
????var?num1?=?document.getElementById("txt2").value;???//獲取第二個輸入框的值
????var?op?=?document.getElementById("select").value;???//獲取選擇框的值
????var?result;
????switch(op)
????????{
????????????case?"+":
????????????????result?=?parseInt(num1)?+?parseInt(num2);
????????????????break;
????????????case?"-":
????????????????result?=?parseInt(num1)?-?parseInt(num2);
????????????????break;
????????????case?"*":
????????????????result?=?parseInt(num1)?*?parseInt(num2);
????????????????break;
????????????case?"/":
????????????????result?=?parseInt(num1)?/?parseInt(num2);
????????????????break;
????????????default:
????????????????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?=?result;//設置結果輸入框的值?
????
???}
??</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?=?按鈕來調用創建的函數，得到結果-->?
???<input?type='text'?id='fruit'?/>???
?</body>
</html>

還請大家幫忙看看，所有的id我都按照原案例寫的，
onclick事件也寫了，邏輯我看應該沒錯吧？