求幫忙，哪里錯了喃，就是運行不出來
<!DOCTYPE html>
<html>
?<head>
? <title> 事件</title> ?
? <script type="text/javascript">
?? function count(){
????? ?
??? var num1=document.getElementById("txt1").value;
??? var num1=document.getElementById("txt2").value;
??? var str=document.getElementById("select").value;
??? var str1="";
??? switch (str){
??????? case "+":
??????????? str1=parseFloat(num1) + parseFloat(num2);
??????????? break;
??????? case "-":
??????????? str1=parseFloat(num1) - parseFloat(num2);
??????????? break;
??????? case "*":
??????????? str1=parseFloat(num1) * parseFloat(num2);
??????????? break;
??????? case "/":
??????????? str1=parseFloat(num1) / parseFloat(num2);
??????????? break;
??? }
??? document.getElementById("fruit").value = str1;
?? }
? </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>
2016-05-01
num1 賦值兩次