为什么用prompt输入。不过输入什么，都返回default
<!DOCTYPE HTML>
<html>
<head>
<meta charset="UTF-8" />
<title>练习06</title>
<script>
var myage=prompt("输入成绩");
switch(myage){
case 10:
case 20:
case 30:
case 40:
case 50:
case 60:
document.write("成绩不合格");
break;
case 70:
document.write("成绩及格");
break;
case 80:
document.write("成绩中等");
break;
default:
document.write("请输入成绩");
}
</script>
</head>
<body>
</body>
</html
