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為什么沒有輸出值

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為什么沒有輸出值

JavaScript

Hakumatsu 2017-06-06 16:51:32

<!DOCTYPE html><html>?<head>? <title> 事件</title> ?? <script type="text/javascript">? var? p,q,s,sum;????? p=document.getElementById("txt1").value;????? q=document.getElementById("txt2").value;????? s=document.getElementById("select").value;????? sum;?? function count(){????? switch(s)????? {????????? case"+":sum=parseInt(p)+parseInt(q);????????? break;????????? case"-":sum=parseInt(p)-parseInt(q);????????? break;?????????? case"*":sum=parseInt(p)*parseInt(q);????????? break;?????????? case"/":sum=parseInt(p)/parseInt(q);????????? break;????? }?? }??? document.getElementById("fruit").value=sum;?? ?? </script> ? <style type=text/css>? #txt2{????? width:80px;? }??? #txt1{????? width:80px;? }?? #fruit{????? width:120px;? }? </style>?</head> ?<body>?? <input type='text' id='txt1' /> ?? <select id='select'>?? ??? ?<option value='+'>+</option>?? ??? ?<option value="-">-</option> ?? ??? ?<option value="*">*</option> ?? ??? ?<option value="/">/</option>?? </select><br/><br/>?? <input type='text' id='txt2' />?? <input type='button' value=' = ' onclick="count()"/> <br/><br/> ?? <input type='text' id='fruit' />? ??</body></html>

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3 回答

__innocence

TA貢獻313條經驗獲得超208個贊

function?count()?{
	var?p,?q,?s,?sum;
	p?=?document.getElementById("txt1").value;
	q?=?document.getElementById("txt2").value;
	s?=?document.getElementById("select").value;

	switch?(s)?{
		case?"+":
			sum?=?parseInt(p)?+?parseInt(q);
			break;
		case?"-":
			sum?=?parseInt(p)?-?parseInt(q);
			break;
		case?"*":
			sum?=?parseInt(p)?*?parseInt(q);
			break;
		case?"/":
			sum?=?parseInt(p)?/?parseInt(q);
			break;
	}
	document.getElementById("fruit").value?=?sum;
}

不明白為什么你要把賦值的語句寫在外面，如果寫在外面，你沒有點擊按鈕，它就執行了。

反對回復 2017-06-06

李曉健

TA貢獻1036條經驗獲得超461個贊

<!DOCTYPE?html>
<html>
<head>
????<title>?事件</title>

????<style?type=text/css>
????????#txt2{
????????????width:80px;
????????}
????????#txt1{
????????????width:80px;
????????}
????????#fruit{
????????????width:120px;
????????}
????</style>
</head>
<body>
<input?type='text'?id='txt1'?/>
<select?id='select'>
????<option?value='+'>+</option>
????<option?value="-">-</option>
????<option?value="*">*</option>
????<option?value="/">/</option>
</select><br/><br/>
<input?type='text'?id='txt2'?/>
<input?type='button'?value='?=?'?onclick="count()"/>?<br/><br/><!--通過?=?按鈕來調用創建的函數，得到結果-->
<input?type='text'?id='fruit'?/>

<!--js代碼需要等到html加載完成可以執行?放到最下面是最簡單的方式-->
<script?type="text/javascript">
????var??p,q,s,sum,sum;
????function?count(){
????????//這些值每一次點擊都需要重新獲取的
????????s=document.getElementById("select").value;
????????p=document.getElementById("txt1").value;
????????q=document.getElementById("txt2").value;
????????switch(s)
????????{
????????????case"+":sum=parseInt(p)+parseInt(q);
????????????????break;
????????????case"-":sum=parseInt(p)-parseInt(q);
????????????????break;
????????????case"*":sum=parseInt(p)*parseInt(q);
????????????????break;
????????????case"/":sum=parseInt(p)/parseInt(q);
????????????????break;
????????}
????????//這個賦值每一次點擊都需要重新來的
????????document.getElementById("fruit").value=sum;
????}


</script>
</body>
</html>

看注釋吧

反對回復 2017-06-06

蜂之谷

TA貢獻564條經驗獲得超863個贊

<script?type="text/javascript">
???function?count(){
	???var??p,q,s,sum;
??????p=document.getElementById("txt1").value;
??????q=document.getElementById("txt2").value;
??????s=document.getElementById("select").value;
??????switch(s)
??????{
??????????case"+":sum=parseInt(p)+parseInt(q);
??????????break;
??????????case"-":sum=parseInt(p)-parseInt(q);
??????????break;
???????????case"*":sum=parseInt(p)*parseInt(q);
??????????break;
???????????case"/":sum=parseInt(p)/parseInt(q);
??????????break;
??????}
	??document.getElementById("fruit").value=sum;
???}
????
????
??</script>

反對回復 2017-06-06

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為什么沒有輸出值

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