I have a problem with the php code. But I did not understand what the problem was


#1

This is the error message (!):
Notice: Undefined index: id in C: \ wamp64 \ www \ show the articles.php on line 15.
and i hope to help because iam a beginner programmer!!
thanks!!
this is the code:
show the articles.php :

     <?php

     $connect=mysqli_connect('localhost','root','aim8552','php');
	
     $tbl_name ="thread";		
	
     $adjacents = "4";
	
     $query="SELECT COUNT(*) as num FROM $tbl_name";
     $total_pages=mysqli_fetch_array(mysqli_query($connect,$query));
     $total_pages=$total_pages["num"];


     $targetpage="show the articles.php";
     $limit=5;
         $page = $_GET["page"]; 

    if($page)
	     $start=($page -1) * $limit;
    else
	     $start=0;

    $sql="SELECT id,topic FROM $tbl_name ORDER BY id DESC LIMIT  $start, 
    $limit";
    $result=mysqli_query($connect,$sql) or die ("error: 
    ".mysqli_error($connect));

    if($page==0) $page=1;
    $prev=$page-1;
    $next=$page+1;
    $lastpage=ceil($total_pages/$limit);

    $lpml=$lastpage-1;

    $pagination="";
    if($lastpage > 1){

	     $pagination.="<div=\"pagination\">";

	     if($page > 1)
		      $pagination.="<a href=\"$targetpage?page=$prev\"> previous</a>";
		  else
			  $pagination.= "<span class=\"disabled\">previous</span>";	
		
		//pages	
	 	if ($lastpage < 7 + ($adjacents * 2))	//not enough pages to bother 
        breaking it up
		{	
			for ($counter = 1; $counter <= $lastpage; $counter++)
			{
				if ($counter == $page)
					$pagination.= "<span class=\"current\">$counter</span>";
				else
					$pagination.= "<a href=\"$targetpage? 
       page=$counter\">$counter</a>";					
			}
		}
		elseif($lastpage > 5 + ($adjacents * 2))	//enough pages to hide some
		{
			//close to beginning; only hide later pages
			if($page < 1 + ($adjacents * 2))		
			{
				for ($counter = 1; $counter < 4 + ($adjacents * 2); $counter++)
				{
					if ($counter == $page)
						$pagination.= "<span class=\"current\">$counter</span>";
					else
						$pagination.= "<a href=\"$targetpage? 
        page=$counter\">$counter</a>";					
				}
				$pagination.= "...";
				$pagination.= "<a href=\"$targetpage?page=$lpm1\">$lpm1</a>";
				$pagination.= "<a href=\"$targetpage? 
       page=$lastpage\">$lastpage</a>";		
			}
			//in middle; hide some front and some back
			elseif($lastpage - ($adjacents * 2) > $page && $page > ($adjacents * 
       2))
			{
				$pagination.= "<a href=\"$targetpage?page=1\">1</a>";
				$pagination.= "<a href=\"$targetpage?page=2\">2</a>";
				$pagination.= "...";
				for ($counter = $page - $adjacents; $counter <= $page + 
       $adjacents; $counter++)
				{
					if ($counter == $page)
						$pagination.= "<span class=\"current\">$counter</span>";
					else
						$pagination.= "<a href=\"$targetpage? 
     page=$counter\">$counter</a>";					
				}
				$pagination.= "...";
				$pagination.= "<a href=\"$targetpage?page=$lpm1\">$lpm1</a>";
				$pagination.= "<a href=\"$targetpage? 
      page=$lastpage\">$lastpage</a>";		
			}
			//close to end; only hide early pages
			else
			{
				$pagination.= "<a href=\"$targetpage?page=1\">1</a>";
				$pagination.= "<a href=\"$targetpage?page=2\">2</a>";
				$pagination.= "...";
				for ($counter = $lastpage - (2 + ($adjacents * 2)); $counter <= 
       $lastpage; $counter++)
				{
					if ($counter == $page)
						$pagination.= "<span class=\"current\">$counter</span>";
					else
						$pagination.= "<a href=\"$targetpage? 
      page=$counter\">$counter</a>";					
				}
			}
		}
		
		//next button
		if ($page < $counter - 1) 
			$pagination.= "<a href=\"$targetpage?page=$next\">next </a>";
		else
			$pagination.= "<span class=\"disabled\">next </span>";
		$pagination.= "</div>\n";		
	    }
       ?>
      <form action="show the articles.php" method="post">
       <?php

		
	
		// Your while loop here
	   echo"<table border='1' width='20%' cellpadding='0' cellspacing='0'>";
       ?>
	   <tr>
        <td>id</td>
        <td>topic</td>
        <td>#</td>
        <td>#</td>
        <td>#</td>
       </tr>
       <?php
       while($row=mysqli_fetch_object($result)){
    	
       ?>
      <tr>
      	 <td><?php echo $row->id; ?></td>
    	 <td><?php echo $row->topic; ?></td>
    	 <td><a href='edit.php?id=<?php echo $row->id; ?>'>edit article</a></td>
    	 <td><input type="checkbox" name="checkbox[]" value="<?php echo $row- 
       >id; ?>"></td>
    	 <td><input type="submit" name="delete" value="delete article"></td>
      </tr>
      <?php
      }
     echo"</table>";
     $num=mysqli_num_rows($result);
     if(isset($_POST['delete'])){
	 for($i=0;$i<$num;$i++){
		$del_id=checkbox[$i];
		$sql2="DELETE FROM thread WHERE id=55";
		$query2=mysqli_query($connect,$sql2);
	  }

     if($query){
	 echo"<meta http-equiv=\"refresh\"content=\"0;URL=del.php\">";
     }



	   }
	
      ?>
     </form>
     <?=$pagination?>