求电脑高手，给做一个PHP程序，急！！ 满意后追加悬赏！！

<?php
//is_uploaded_file()函数的作用是：判断文件是否是通过HTTPPOST上传的
/*
if(is_uploaded_file($_FILES['userfile']['tmp_name']))
{
$upfile =$_FILES['userfile'];
$name =$upfile['name'];
$type =$upfile['type'];
$size =$upfile['size'];
$tmp_name =$upfile['tmp_name'];
$error =$upfile['error'];
switch($type)
{
case
}
if(move_uploaded_file($tmp_name,"images/".$name))
{
echo '上传成功';
}
else
{
echo "上传失败";
}
}
*/
if(isset($_FILES['userfile']))
{
if(is_uploaded_file($_FILES['userfile']['tmp_name']))
{
$upfile=$_FILES['userfile'];
$name=$upfile['name'];
$type=$upfile['type'];
$tmp_name=$upfile['tmp_name'];
$size=$upfile['size'];
$error=$upfile['error'];

/*过滤文件一是根据type类型
二是根据扩展名
*/
/*
switch($type)
{
case "image/pjpeg":$ok=1;
break;
case "image/jpeg":$ok=1;
break;
case "image/gif":$ok=1;
break;
case "image/png";$ok=1;
break;
}
*/
$extenName=end(explode('.',$name));
switch($extenName)
{
case "jpg";
case "bmp";
case "gif";
case "png";
$ok=1;
break;
}
if($ok==1)
{
$doc_root=$_SERVER['DOCUMENT_ROOT'];
if(!file_exists($doc_root."/upload/images"))//检测上传目录是否存在，如果不存在就创建该目录
{
mkdir("images");
}
if(move_uploaded_file($tmp_name,$doc_root."/upload/images/".$name))
{
echo "上传成功";
}
else
{
echo "上传失败";
}
}
else
{
echo "上传类型有误，请重新选择类型";
}
}
}
?>
<meta http-equiv="Content-Type" content="texst/html;charset=gb2312"/>
<center>
<form name="upload" id="upload" enctype="multipart/form-data" method="post">
上传文件:<input type='file' name='userfile'/>
<input type="submit" name="upload" value="上传"/>
</form>
<br>
<b>上传的文件</b>
</center>

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