Q:

stored checkbox values fetch and keep checkbox selected

I store my checkbox values in a field name tagpost and they are saved as tag1,tag2,tag3,tag4, now I have managed to fetch them: 
        $tg = $row['tagpost '];
        $tg1 = explode(',', $tg);
        $tg2 = implode(" ",$tg1);

But the issue I face now is how do I keep the values selected?
Here is my php part from the form:
enter image description here
 <?php //include config
require_once('../includes/config.php');

//if not logged in redirect to login page
if(!$user->is_logged_in()){ header('Location: login.php'); }
?>
<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Admin - Edit Post</title>
  <link rel="stylesheet" href="../style/normalize.css">
  <link rel="stylesheet" href="../style/main.css">
  <script src="//tinymce.cachefly.net/4.0/tinymce.min.js"></script>
  <script>
          tinymce.init({
              selector: "textarea",
              plugins: [
                  "advlist autolink lists link image charmap print preview anchor",
                  "searchreplace visualblocks code fullscreen",
                  "insertdatetime media table contextmenu paste"
              ],
              toolbar: "insertfile undo redo | styleselect | bold italic | alignleft aligncenter alignright alignjustify | bullist numlist outdent indent | link image"
          });
  </script>
  <script type="text/javascript">
    function delete_id_img(id)
    {
        if(confirm('Do you really want to delete this image?'))
        {
            window.location.href='edit-post.php?act=deleteimg&id='+id;
        }
    }
    </script>
</head>
<body>

<div id="wrapper">

    <?php include('menu.php');?>
    <p><a href="./">Blog Admin Index</a></p>

    <h2>Edit Post</h2>

    <?php

    //if form has been submitted process it
    if(isset($_POST['submit'])){

        $_POST = array_map( 'stripslashes', $_POST );

        //collect form data
        extract($_POST);

        //very basic validation
        if($postID ==''){
            $error[] = 'This post is missing a valid id!.';
        }

        if($postTitle ==''){
            $error[] = 'Please enter the title.';
        }

        if($postCat ==''){
            $error[] = 'Please select category.';
        }

        if($postDesc ==''){
            $error[] = 'Please enter the description.';
        }

        if($postCont ==''){
            $error[] = 'Please enter the content.';
        }

        if(!isset($error)){

         $st = "SELECT * FROM blog_posts WHERE postID = :postID";
        $st = $db->prepare($st);
        $st->bindParam(':postID', $postID, PDO::PARAM_STR);
        $st->execute();
        $rm = $st->fetch();
        $count = $st->rowCount();

        if($_FILES['file']['name']!='')
        {
                $file='../uploads/images/'.$rm['postImg'];
                @unlink($file);              
                $tmp_name = $_FILES["file"]["tmp_name"];
                $namefile = $_FILES["file"]["name"];
                $ext = end(explode(".", $namefile));
                $fileUpload = move_uploaded_file($tmp_name,"../uploads/images/".$image_name);
                $image_name=time().".".$ext;                
                watermark_image($tmp_name,"../uploads/images/".$image_name);
                $img = ''.$image_name.'';
            }else{
                $img = $rm['postImg'];
            }

            try {

                $postSlug = slug($postTitle);

                //insert into database
                $stmt = $db->prepare('UPDATE blog_posts SET postTitle = :postTitle, postImg = :postImg, postYoutube = :postYoutube, postSlug = :postSlug, postDesc = :postDesc, postCont = :postCont, postCat = :postCat WHERE postID = :postID') ;
                $stmt->execute(array(
                    ':postTitle' => $postTitle,
                    ':postImg' => $img,
                    ':postYoutube' => $postYoutube,
                    ':postSlug' => $postSlug,
                    ':postDesc' => $postDesc,
                    ':postCont' => $postCont,
                    ':postCat' => $postCat,
                    ':postID' => $postID
                ));

                  $seturl = "".$postID."/".$postSlug."";
                  $qry2 = "UPDATE blog_posts SET postSlug = :postSlug WHERE postID = :postID";
                  $statement = $db->prepare($qry2);               
                  $statement->bindParam(':postSlug', $seturl);      
                  $statement->bindParam(':postID', $postID);            
                  $statement->execute();

                //redirect to index page
                header('Location: edit-post.php?id='.$postID.'');   
                exit;

            } catch(PDOException $e) {
                echo $e->getMessage();
            }

        }

    }

    ?>

    <?php
    //check for any errors
    if(isset($error)){
        foreach($error as $error){
            echo $error.'<br />';
        }
    }

        try {

            $stmt = $db->prepare('SELECT postID, postTitle, postImg, postYoutube, postDesc, postCont, postYoutube, postTag, postCat FROM blog_posts WHERE postID = :postID') ;
            $stmt->execute(array(':postID' => $_GET['id']));
            $row = $stmt->fetch(); 

            $tg = $row['postTag'];
            $tg1 = explode(',', $tg);
            $tg2 = implode(',', $tg1);

        } catch(PDOException $e) {
            echo $e->getMessage();
        }

    ?>

    <?php
 $act = $_REQUEST['act'];
     $id = $_REQUEST['id'];
     if($act == "deleteimg")
     { 
         //$qry = "SELECT * FROM  article where id IN(".$id.")";
         //$result = mysql_query($qry);
         $qry = "SELECT * FROM  blog_posts WHERE postID IN(:postID)";
         $stmt = $db->prepare($qry);
         $stmt->bindParam(':postID', $id);
         $stmt->execute();      
         while( $row = $stmt->fetch())
         {
             $file='../uploads/images/'.$row['postImg'];
             @unlink($file);
         }

        //$sqlAdd ="update article set ne_image = '' where id IN(".$id.")";
        //mysql_query($sqlAdd); 
         $qr = "UPDATE blog_posts SET postImg = '' WHERE postID IN(:postID)";
         $statement = $db->prepare($qr);
         $statement->bindParam(':postID', $id);
         $statement->execute();
        //header("Location:post-article.php?id=".$id."");
        header('Location: edit-post.php?id='.$id.'');       
     }
      ?>

      <?php 
    //show message 
    if(isset($_GET['action'])){ 
        echo '<h3>Post '.$_GET['action'].'.</h3>'; 
    } 
    ?>

    <?php  if(!empty($row['postImg'])){ echo '<img src="../uploads/images/'.$row['postImg'].'"><br/><a href="javascript:delete_id_img('.$row['postID'].')">Delete</a><br/>'; }else{ echo'<br/>'; } 
?>

<?php  if(!empty($row['postYoutube'])){ echo '<iframe width="720" height="450" src="http://www.youtube.com/embed/'.$row['postYoutube'].'"></iframe><br/><br/>'; }else{ echo'<br/>'; } 
?>

    <form action='' method='post' enctype="multipart/form-data">
        <input type='hidden' name='postID' value='<?php echo $row['postID'];?>'>

        <p><label>Title</label><br />
        <input type='text' name='postTitle' value='<?php echo $row['postTitle'];?>'></p>

        <p><label>Category</label><br />
        <select name="postCat">
                <option value="" selected="selected" disabled="disabled">Select Category</option>
                    <?php                   
                    $stmt = $db->prepare('select * from blog_categories');
                    $stmt->execute();
                    $rc = $stmt->fetchAll();
                    foreach($rc as $rows){
                    ?>
                    <option value="<?php echo $rows['catUrl']; ?>" <?php if($row['postCat'] == ''.$rows['catUrl'].'') echo 'selected="selected"'; ?>><?php echo $rows['catName']; ?></option>

                    <?php
                    }
                    ?>
                </select>
                </p>

        <?php if(!empty($row['postYoutube'])){
        ?>

        <?php   
        }else{
        ?>      
        <p><label>Image</label><br />
        <input type="file" name="file" id="file"/>  </p>
        <?php   
        }
        ?>      
        <?php if(!empty($row['postImg'])){
        ?>

        <?php   
        }else{
        ?>          

        <p><label>Youtube Video ID</label><br />
        <input type="text" name="postYoutube" id="postYoutube" placeholder="Video ID e.g. lQem15Ow6hw"  value="<?php echo $row['postYoutube'];?>" />    </p>
        <?php   
        }
        ?>          

        <p><label>Description</label><br />
        <textarea name='postDesc' cols='60' rows='10'><?php echo $row['postDesc'];?></textarea></p>

        <p><label>Content</label><br />
        <textarea name='postCont' cols='60' rows='10'><?php echo $row['postCont'];?></textarea></p>

        <br/>
        <p><label>Tags <small></small></label><br /><br />
        <?php                   
                    $stmt = $db->prepare('select * from blog_tag');
                    $stmt->execute();
                    $rt = $stmt->fetchAll();
                    foreach($rt as $rtg){
                    ?>
                    (<input type="checkbox" name="postTag[]" value="<?php echo $tg2; ?>" <?php if(in_array($rtg['tagurl'],$tg1)){ echo 'checked="checked"'; } ?>> <?php echo $rtg['tagName']; ?>) , 

                    <?php                                   
                    }
                    ?>
        <br/>

        <p><input type='submit' name='submit' value='Update'></p>

    </form>

</div>

</body>
</html> 

The code above fetches all tag names from blog_tags and tries to compare it with tagpost inside posts.

A:

Simple use IN_ARRAY <?= (in_array($rtg['tagName'],$tg1))? 'checked="checked"' : "" ?>
$tg = $row['tagpost'];
$tg1 = explode(',', $tg);

..........

foreach($rt as $rtg){
?>
<input type="checkbox" name="postTag[]" value="<?php echo $rtg['tagurl']; ?>"  <?php if(in_array($rtg['tagurl'],$tg1)){ echo 'checked="checked"'; } ?> > <?php echo $rtg['tagName']; ?>

<?php                   
}

