php webmail中的switch($ action)错误

I am trying to send emails using php

<HTML>
<HEAD><TITLE>E-mailer</TITLE></HEAD>
<BODY background="bricks.jpg">
<?php
//adv_mailer.php

function mailer_header()
{
?>
<p>
<?php
}

function mailer_footer()
{
?>
<p>
<?php
}

function error_message($msg)
{
   mailer_header();
   echo "<SCRIPT>alert(\"Error: $msg\");history.go(-1)</SCRIPT>";
   mailer_footer();
   exit;
}

function user_message($msg)
{
   mailer_header();
   echo "<SCRIPT>alert(\"$msg\");history.go(-1)</SCRIPT>";
   mailer_footer();
   exit;
}

function mail_form() {
   global $PHP_SELF;
?>
<FORM METHOD="POST" ENCTYPE="MULTIPART/FORM-DATA" ACTION="<?php echo $PHP_SELF ?>">
<INPUT TYPE="HIDDEN" NAME="action" VALUE="send_mail">
<DIV ALIGN="CENTER ">
<TABLE CELLSPACING="2" CELLPADDING="5" WIDTH="79%" BORDER="0">
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">To</font></TH>
      <TD WIDTH="84%" colspan="2"><font color="#FFFF00"><INPUT NAME="mail_to" SIZE="81"></font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">Cc</font></TH>
      <TD WIDTH="84%" colspan="2"><font color="#FFFF00"><INPUT NAME="mail_cc" SIZE="81"></font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">Bcc</font></TH>
      <TD WIDTH="84%" colspan="2"><font color="#FFFF00"><INPUT NAME="mail_bcc" SIZE="81"></font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">From</font></TH>
      <TD WIDTH="84%" colspan="2"><font color="#FFFF00"><INPUT SIZE="81" NAME="mail_from"></font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">Reply-to</font></TH>
      <TD WIDTH="84%" colspan="2"><font color="#FFFF00"><INPUT SIZE="81" NAME="mail_reply_to"></font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">Attachment</font></TH>
      <TD WIDTH="84%" colspan="2"><font color="#FFFF00"><INPUT TYPE="FILE" NAME="userfile"></font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">Type</font></TH>
      <TD WIDTH="23%">
      <font color="#FFFF00">
      <INPUT TYPE="RADIO" VALUE="text" NAME="mail_type" CHECKED>TEXT</font></TD>
      <TD WIDTH="61%">
      <font color="#FFFF00">
      <INPUT TYPE="RADIO" VALUE="html" NAME="mail_type">HTML</font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">Encoding</font></TH>
      <TD WIDTH="23%">
      <font color="#FFFF00">
      <INPUT TYPE="RADIO" VALUE="7bit" NAME="mail_encoding" CHECKED>7BIT</font></TD>
      <TD WIDTH="61%">
      <font color="#FFFF00">
      <INPUT TYPE="RADIO" VALUE="8bit" NAME="mail_encoding">8BIT</font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">Character Set</font></TH>
      <TD WIDTH="23%">
      <font color="#FFFF00">
      <INPUT TYPE="RADIO" VALUE="us-ascii" NAME="mail_charset" CHECKED>US-ASCII&nbsp;</font></TD>
      <TD WIDTH="61%">
      <font color="#FFFF00"><INPUT TYPE="RADIO" VALUE="euc-kr" NAME="mail_charset">EUC-KR</font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%"><font color="#FFFF00">Subject</font></TH>
      <TD WIDTH="84%" colspan="2"><font color="#FFFF00"><INPUT SIZE="81" NAME="mail_subject"></font></TD>
   </TR>
   <TR>
      <TH ALIGN="right" WIDTH="16%" valign="top"><font color="#FFFF00">Body</font></TH>
      <TD WIDTH="84%" colspan="2"><TEXTAREA NAME="mail_body" ROWS="16"
         COLS="62"></TEXTAREA></TD>
   </TR>
   <TR>
      <TH WIDTH="100%" COLSPAN="3" ALIGN="CENTER">
         <INPUT TYPE="SUBMIT" VALUE="Send" NAME="SUBMIT">
         <INPUT TYPE="RESET" VALUE="Reset" NAME="RESET">
      </TH>
   </TR>
</TABLE>
</DIV>
</FORM>
<?php
}

function send_mail()
{
   global $mail_to, $mail_cc, $mail_bcc, $mail_from, $mail_reply_to;
   global $mail_body, $mail_subject;
   global $userfile, $userfile_type, $userfile_name, $userfile_size;
   global $mail_type, $mail_charset, $mail_encoding;

   $mail_parts["mail_type"] = $mail_type;
   $mail_parts["mail_charset"] = $mail_charset;
   $mail_parts["mail_encoding"] = $mail_encoding;

   $mail_parts["userfile"] = $userfile;
   $mail_parts["userfile_type"] = $userfile_type;
   $mail_parts["userfile_name"] = $userfile_name;
   $mail_parts["userfile_size"] = $userfile_size;


   $mail_parts["mail_to"] = $mail_to;
   $mail_parts["mail_from"] = $mail_from;
   $mail_parts["mail_reply_to"] = $mail_reply_to;
   $mail_parts["mail_cc"] = $mail_cc;
   $mail_parts["mail_bcc"] = $mail_bcc;
   $mail_parts["mail_subject"] = trim($mail_subject);
   $mail_parts["mail_body"] = $mail_body;

   if(my_mail($mail_parts))
      user_message("Successfully sent an e-mail titled '$mail_subject'.");

   else error_message("An unknown error occurred while attempting to
                                 send an e-mail titled '$mail_subject'.");
}

function my_mail($mail_parts)
{
   $mail_to = $mail_parts["mail_to"];
   $mail_from = $mail_parts["mail_from"];
   $mail_reply_to = $mail_parts["mail_reply_to"];
   $mail_cc = $mail_parts["mail_cc"];
   $mail_bcc = $mail_parts["mail_bcc"];
   $mail_subject = $mail_parts["mail_subject"];
   $mail_body = $mail_parts["mail_body"];

   $mail_type = $mail_parts["mail_type"];
   $mail_charset = $mail_parts["mail_charset"];
   $mail_encoding = $mail_parts["mail_encoding"];

   $userfile = $mail_parts["userfile"];
   $userfile_type = $mail_parts["userfile_type"];
   $userfile_name = $mail_parts["userfile_name"];
   $userfile_size = $mail_parts["userfile_size"];

   if(empty($mail_to)) error_message("Empty to field!");
   if(empty($mail_subject)) error_message("Empty subject!");
   if(empty($mail_body)) error_message("Empty body! ");

   $mail_to = str_replace(";", ",", $mail_to);

   $mail_headers = '';

   if(!empty($mail_from)) $mail_headers .= "From: $mail_from
";
   if(!empty($mail_reply_to)) $mail_headers .= "Reply-to: $mail_reply_to
";
   if(!empty($mail_cc))
            $mail_headers .= "Cc: " . str_replace(";", ",", $mail_cc) . "
";
   if(!empty($mail_bcc))
            $mail_headers .= "Bcc: " . str_replace(";", ",", $mail_bcc) . "
";

   $mail_subject = stripslashes($mail_subject);
   $mail_body = stripslashes($mail_body);

   if($userfile_size > 0)
   {
      $mail_boundary = md5(uniqid(time()));
      $mail_headers .= "MIME-Version: 1.0
";
      $mail_headers .= "Content-type: multipart/mixed;
                                      boundary=\"$mail_boundary\"

";
      $mail_headers .= "This is a multi-part message in MIME format.

";

      $fp = fopen($userfile, "r");
      $file = fread($fp, filesize($userfile));
      $file = chunk_split(base64_encode($file));

      $new_mail_body = "--$mail_boundary
";
      $new_mail_body .= "Content-type:text/plain;charset=$mail_charset
";
      $new_mail_body .= "Content-transfer-encoding:$mail_encoding

";
      $new_mail_body .= "$mail_body
";
      $new_mail_body .= "--$mail_boundary
";
      if(!empty($userfile_type)) $mime_type = $userfile_type;
      else $mime_type = "application/octet-stream";

      $new_mail_body .= "Content-type:$mime_type;name=$userfile_name
";
      $new_mail_body .= "Content-transfer-encoding:base64

";
      $new_mail_body .= $file . "

";
      $new_mail_body .= "--$mail_boundary--";
      $mail_body = $new_mail_body;
   }
   else if($mail_type == 'html')
   {
      $mail_headers .= "Content-type: text/html; charset=$mail_charset
";
      $mail_headers .= "Content-transfer-encoding:$mail_encoding

";
   }
   else
   {
      $mail_headers .= "Content-type: text/plain; charset=$mail_charset
";
      $mail_headers .= "Content-transfer-encoding:$mail_encoding

";
   }

   return mail($mail_to,$mail_subject,$mail_body,$mail_headers);
}
switch ($action)
{
   case "send_mail":
     mailer_header();
     send_mail();
     mailer_footer();
     break;
case "mail_form":
    mailer_header();
    mail_form();
     mailer_footer();
      break;
   default:
      mailer_header();
      mail_form();
      mailer_footer();
      break;
}

?>
</BODY>
</HTML>

I keep getting this errors Notice: Undefined variable: action in C:\wamp\www\5\adv_mail.php on line 226 Notice: Undefined variable: action in C:\wamp\www\5\adv_mail.php on line 231

any help would be appreciated

$action is surely undefined. From your code it appears like you expect that to be the HTML hidden field named action that you've defined in your form. That error is simply saying you are trying to run a switch statement on something that doesn't exist. For that you should initialize it first.

if(isset($_POST['action']))
  $action = $_POST['action'];  // This is missing
else
  die("No action defined");

switch ($action)
{
....
}