How to check if an admin

if (isset($userdata['user_id']) && $userdata['user_id'] == $writerId)
  {
      opentable("Manage code");
    echo ('<div style="text-align: center;"><form method="post" action="submitcode.php"><input type="hidden" value="'.$id.'" name="code" /><input type="submit" name="edit" value="Edit Code" class="button" /></form></div>');
    $result = mysql_query("SELECT id,name FROM KeyeD_codename");
    echo "<div style=\"text-align: center;\"><form method=\"post\" action=\"codebank.php?type=".$row['Type']."\"><input type=\"hidden\" value=\"".$id."\" name=\"code\" /><input type=\"submit\" name=\"delete\" value=\"Delete Code\" class=\"button\" /></form>   \n";
     
      echo "</div>";
      closetable();
  }
  else{
  }
}