php - undefined variable $url, unsure why I am getting this error -

can tell me why getting following undefined variable ($url) error script. error if statement if ($url). newbie. thanks

an error occurred in script 'testnew/edit_your_sites.php' on line 28: undefined variable: url

<div class="text">     <?php     $page_title = 'edit account';     include ('includes/header.html');     include ('includes/functions.php');     include ('includes/config.inc.php');     if (isset($_get['id']) && is_numeric($_get['id'])){         $id = $_get['id'];     } elseif (isset($_post['id']) && is_numeric($_post['id'])) {         $id = $_post['id'];     } else {         echo '<p class="error">this page has been accessed in error.</p>';         include ('includes/footer.html');         exit();     }     if (isset($_session['userid'])){     require (mysql);     $scrubbed = array_map('spam_scrubber', $_post);       if ($_server['request_method'] == 'post'){     if (empty($scrubbed['url'])){             echo '<p class="error">please enter url</p>';         } else {             $url = mysqli_real_escape_string($dbc, $scrubbed['url']);         }     }     if ($url){     $p = "select userid sites userid=$id";     $q = mysqli_query($dbc, $p);     if (mysqli_num_rows($q) == 1){      $i = "insert sites (userid, url, entry) values('{$_session['userid']}', '$url', now())";     $r = mysqli_query($dbc, $i);         if (mysqli_affected_rows($dbc) == 1){         echo '<p>your website added succesfully.</p>';         } else {             echo '<p class="error">due system error website not added.</p>';         }      } else {         echo '<p class="error">please try again';     }      }     ?>     <form action="edit_your_sites.php" method="post">     <?php $sql = "select * sitetypes";     $f = mysqli_query($dbc, $sql) or trigger_error("query: $sql\n<br />mysqli error: " . mysqli_error($dbc));     echo '<select name="sitetype" selected="selected">';     while($row2 = mysqli_fetch_array($f, mysqli_assoc)){         if ($row2['sitetype'] == 'selected'){             echo "<option selected='selected' value=" . $row2["sitetypeid"] . ">" . $row2['sitetype'] . "</option>";         } else {              echo "<option value=" . $row2["sitetypeid"] . ">" . $row2['sitetype'] . "</option>";         }     }      echo '</select>';     ?>     <p>url:<input type="text" name="url" size="30" maxlength="60" value="<?php if(isset($scrubbed['url'])) echo $scrubbed['url']; ?>" /></p>     <?php     echo '</fieldset>     <p><input type="submit" name="submit" value="edit account!" /><input type="reset" name="reset" value="clear form" />     <input type="hidden" name="id" value="' . $id . '" />     </form>';     } else {         $url = base_url . 'index.php';         header("location: $url");     }     ?> 

there may more errors in script if see appreciated if let me know them. help, guys great help

the variable defined within if statement, need define prior that... try defining blank value @ beginning of script.

$page_title = 'edit account'; $url=""; include ('includes/header.html');