<!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 num1=parseInt(document.getElementById('txt1').value);
//获取第二个输入框的值
var num1=parseInt(document.getElementById('txt2').value);
//获取选择框的值
var select=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 answer;
switch(select){
case '+':
answer=num1+num2;
break;
case '-':
answer=num1-num2;
break;
case '*':
answer=num1*num2;
break;
case '/':
answer=num1/num2;
break;
default:
answer=0;
break;
}
//设置结果输入框的值
document.getElementById('fruit').value=answer;
}
</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>
