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Javascript進階篇6-11的編程練習

<!DOCTYPE?html>
<html>
<head>
<meta?charset="UTF-8">
<title>JS進階篇編程練習</title>
<script?type?=?"text/Javascript">
function?count(){
	//獲取第一個輸入框的值,parseInt防止獲取的為字符串
	?var?txt1?=?parseInt(document.getElementById("txt1").value);?
	//獲取第二個輸入框的值
	?var?txt2?=?parseInt(document.getElementById("txt1").value);??
	//獲取選擇框的值
	var?txt3?=?document.getElementById("select").value;
	
	//獲取通過下拉框來選擇的值來改變加減乘除運算
	switch(tet3){
	case?"+":sum?=?txt1?+?txt2;?break;
	case?"-":sum?=?txt1?-?txt2;?break;
	case?"*":sum?=?txt1?*?txt2;?break;
	case?"/":sum?=?txt1?/?txt2;?break;
	}
	//設置輸入框的值
	getElementById("friut").value?=?sum;
}
</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>

運行完點擊=沒結果?。吭趺椿厥履?？親們