<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
//获取第一个输入框的值
//获取第二个输入框的值
//获取选择框的值
//获取通过下拉框来选择的值来改变加减乘除的运算法则
//设置结果输入框的值
var num1 = document.getElementById("txt1").value;
var num2 = document.getElementById("txt2").value;
var sign = document.getElementById("select").value;
var result = 0;
switch (sign)
{
case "+":
result = parselnt(num1) + parselnt(num2);
break;
case "-":
result = parselnt(num1) - parselnt(num2);
break;
case "*":
result = parselnt(num1) * parselnt(num2);
break;
case "/":
result = parselnt(num1) / parselnt(num2);
break;
}
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()"/> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit' />
</body>
</html>
switch写错了,改成这样
switch(z){
case "+":
document.getElementById("fruit").value=Number(x)+Number(y);
break;
case "-":
document.getElementById("fruit").value=Number(x)-Number(y);
break;
case "*":
document.getElementById("fruit").value=Number(x)*Number(y);
break;
case "/":
document.getElementById("fruit").value=Number(x)/Number(y);
break;
}