文件上传下载php

I am writing a script for file upload to a MySQL db. I get an error saying : Notice: Undefined variable: code in C:\wamp\www\application\letters.php on line 82 This is the word code which is in **. Anyone that can spot the mistake please let me know.

if ($name)
    if ($title && $description)
        {       
            $date = date("d m Y");
            $charset ="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

            //length of value to generate
            $length = 15;

            //create variable and run through and randomly select fromcharset.
            for ($i = 0; $i <= $length; $i++)
            {   
                //position to start at. rand function.
                $rand = rand() % strlen($charset);
                $tmp = substr($charset, $rand, 1);

                //append onto code
                **$code .= $tmp;**
            }
            //checking for existence of code which is generated. 
            $query= mysql_query("SELECT code FROM letter_details WHERE code = '$code'");

            //if code is found
            $numrows = mysql_num_rows($query);

            // if that code exists, generate code again
            while ($numrows != 0)
            {
                for ($i=0; $i <= $length; $i++)
                {
                    //position to start at. rand function.
                    $rand = rand() % strlen($charset);
                    $tmp = substr($charset, $rand, 1);

                    //append onto code
                    $code .=$tmp;
                }

                //checking for existence of code which is generated.
                $query= mysql_query("SELECT code FROM letter_details WHERE code = '$code'");

                //if code is found
                $numrows = mysql_num_rows($query);
            }

            //create directory
            mkdir("files/$code");

            //put file into it
            move_uploaded_file($tmpname, "files/$code/"."$name".$ext);
            $query = mysql_query("INSERT INTO letter_details VALUES ('$letter_id', $title','$code','$description','$student_info_id', '$staff_info_id', '$date')");
            echo "Your file '$title' was Succesfully uploaded.<br><br><a href='download.php?file=$code'>Download</a>";

You must define $code before adding more into to it by $code .= '' (put $code = ''; before loop)

Add a $code=''; outside the for loop.Variables are to be declared in such cases,ie concatenation operation, before they are used.

If you want to read a variable outside a for loop you must define it before.

This is notice which warns you regarding undefined variables.

The execution of program does not affect by notice. To fix this you can initialize the $code variable somewhere in the starting of the script like $code = '';

Here is the snippet of code you must use in your script for uploading files:

<?php
$uploads_dir = '/uploads';
foreach ($_FILES["pictures"]["error"] as $key => $error) {
    if ($error == UPLOAD_ERR_OK) {
        $tmp_name = $_FILES["pictures"]["tmp_name"][$key];
        $name = $_FILES["pictures"]["name"][$key];
        move_uploaded_file($tmp_name, "$uploads_dir/$name");
    }
}
?>

Check and see if it works for you.