运行不出结果
<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
//获取第一个输入框的值
var a1 = document.getElementById("txt1").value;
//获取第二个输入框的值
var a2 = document.getElementById("txt2").value;
//获取选择框的值
var a3 = document.getElementById("select").value;
//获取通过下拉框来选择的值来改变加减乘除的运算法则
var a4=0;
switch(a3){
case '+':
a4 = a1+a2;
return a4;
break;
case '-':
a4 = a1-a2;
return a4;
break;
case '*':
a4 = a1*a2;
return a4;
break;
case '/':
a4 = a1/a2;
return a4;
break;
}
//设置结果输入框的值
document.getElementById("fruit").value = a4;
}
</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()"/> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit'/>
</body>
</html
