im going to make an algorithm menu with this code on index.php

```
 <?php
$menu=$_GET[menu];
$file=$_GET[file];

if(!isset($menu))
{
    $menu="home";
}
if(($menu=="'")||($menu="-")||($menu="/"))
{
    $menu="home";
}
switch($menu)
{
    case'home':
        $file="isi/home.html";
    break;
    case'profile':
        $file="isi/profile.html";
    break;
    case'gallery':
        $file="isi/lihat_bukutamu.php";
    break;
    case'download':
        $file="isi/lihat_bukutamu.php";
    break;
    case'contact':
        $file="isi/buku_tamu.php";
    break;
}
include"header.php";
include"menu.php";
include"content.php";
include"footer.php";
?>

```

but but when i try this script it show me 

> 
> Notice: Use of undefined constant menu - assumed 'menu' in
>  C:\xampp\htdocs\layout\index.php on line 2
> 
> 
> Notice: Undefined index: menu in C:\xampp\htdocs\layout\index.php on
>  line 2
> 
> 
> Notice: Use of undefined constant file - assumed 'file' in
>  C:\xampp\htdocs\layout\index.php on line 3
> 
> 
> Notice: Undefined index: file in C:\xampp\htdocs\layout\index.php on
>  line 3
> 
> 
> 

this is the menu.php

```
<div id="menu-content">
            <div id="menu">
                <h3 class ="judul_1">Main Menu</h3>
                    <ul>
                        <li><a href="index.php?menu=home">Home</a></li>
                        <li><a href="index.php?menu=profile">Profile</a></li>
                        <li><a href="index.php?menu=gallery">Gallery</a></li>
                        <li><a href="index.php?menu=download">Download</a></li>
                        <li><a href="index.php?menu=contact">Contact</a></li>
                    </ul>
                </div>

```

can you solve it?