老师我没太明白这道题的思路，请老师看看我这写的对不对

来源：3-3 编程练习

努力的大白

2019-05-03 10:32:31

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<form action="#" method="post" >
<span>请输入成绩</span>
<input type="text" placeholder="请输入成绩" name="num">
<input type="submit" name="ok">
</form><?php
header("content-type:text/html;charset=utf-8");
error_reporting(E_ALL&~E_NOTICE);
$scort=$_POST['num'];$get="";
$com =function() {
global $scort;
global $get;
if($_POST['ok']){
if (is_numeric($_POST['num'])){if ($scort <= 100 && $scort >= 80) {
echo $get='优秀';
}elseif($scort <= 80 && $scort >= 60){
echo $get='合格';
}
elseif($scort <= 60 && $scort >= 0){
echo $get='不合格';
}
}else{
echo '请输入有效数字';
}
}else{
exit();
}

} ;

$com();
?>
</body>
</html>