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                        /JavaScript進階篇

想問下同學，為什么我這段代碼可以計算加減，但是乘法和除法計算不出來呢？

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