if(isset($_GET['u'])) {
        $uname = mysqli_real_escape_string($con, $_GET['u']);

     ....

    if(!$posts) {   
            $div_class = 'danger';
            $div_msg = 'Database error: ' . mysqli_error($con);
        } else {
            $post_count = mysqli_num_rows($posts);      
            if($post_count == 0) {
                $page_count = 0;
                $div_class = 'danger';
                $div_msg = "Sorry, no posts found for user <strong>'$uname'</strong>.";
            } else {
                $page_count = ceil($post_count / 8);
                $div_class = 'success';
                $div_msg = " Showing published posts for user <strong>'$uname'</strong>.";
                $div_msg .= " <a href='index.php'>Show All</a>";
            }
        }
    }

if(isset($_POST['submit'])) {
    // clean up inputs
    $username       = mysqli_real_escape_string($con, $_POST['username']);

  ...


    <div class="form-group">
                <label for="username" class="sr-only">Choose a Username</label>
                <input type="text" name="username" class="form-control" 
          value="<?php echo $username;?>" placeholder="Enter Desired Username *">
    </div>

if(isset($_GET['cid'])) {
        $cid = mysqli_real_escape_string($con, $_GET['cid']);

        // find total number of posts to determine number of pages for pagination
        $q = "SELECT * FROM cms_posts where post_cat_id = $cid";
        $result = mysqli_query($con, $q);
        $total_posts = mysqli_num_rows($result);
        $total_pages = ceil($total_posts / POSTSPERPAGE);

        // if $total_pages is 0, set it to 1 so pagination will not look for page 0
        if($total_pages < 1) {
            $total_pages = 1;
        }

  ...

    $q1 = "SELECT cms_posts.*, cms_users.user_image FROM cms_posts
                    INNER JOIN cms_users ON cms_posts.post_author = cms_users.user_uname
                    WHERE post_cat_id = '$cid' 
                    AND post_status = 'Published'
                    ORDER BY post_date DESC " . $limit_clause;

        // get category name from database to display in alert box
        $q2 = "SELECT cat_title FROM cms_categories WHERE cat_id = $cid";

        $result = mysqli_query($con, $q2);
        $cat_title = mysqli_fetch_array($result);

  ...

<?php
if(isset($_GET['source'])) {
    $source = $_GET['source'];
} else {
    $source = "";
}

switch($source) {
    case 'add_user':
        include 'admin_includes/admin_add_user.php';
        break;
    case 'edit_user':
        include 'admin_includes/admin_edit_user.php';
        break;
    case 'c':
        echo 'c';
        break;
    default:
        include 'admin_includes/admin_view_all_users.php';
}

?>

if(isset($_POST['updateusersubmit'])) {
        // get all input data
        $user_id = $_POST['user_id'];
        $user_uname = $_POST['user_uname'];

  ...


        if(empty($user_uname) || empty($user_email) || empty($user_pass1) || empty($user_pass2)) {
            $div_class = 'danger';
            $div_msg = 'Please fill in all required fields.';
        } elseif($user_pass1 !== $user_pass2) {
            $div_class = 'danger';
            $div_msg = 'Password fields do not match.';
        } elseif(!$user_email_val) {
            $div_class = 'danger';
            $div_msg = 'Please enter a valid email address.';       
        } else { 
            // encrypt password (see documentation on php.net)      
            $options =['cost'=>HASHCOST];
            $user_pass = password_hash($user_pass1, PASSWORD_BCRYPT, $options); 

            move_uploaded_file($image_tmp, "../images/$user_image");

            $q = "UPDATE cms_users SET user_uname = '$user_uname', 
                        user_pass = '$user_pass', user_fname = '$user_fname', 
                        user_lname = '$user_lname', user_email = '$user_email',
                        user_image = '$user_image', user_role = '$user_role', 
                        user_status = '$user_status' WHERE user_id = $user_id";

            $result = mysqli_query($con, $q);

      ...

if(isset($_GET['p'])) {
            $page = mysqli_real_escape_string($con, $_GET['p']);

            // the 1st number in LIMIT is a multiple of POSTSPERPAGE starting at 0
            $first_limit = ($page - 1) * POSTSPERPAGE; // POSTSPERPAGE = 10
        } else {
            // $first_limit is needed for LIMIT clause, $page is needed for setting
            // active class of pagination buttons
            $first_limit = 0;
            $page = 1;
        }

        // create LIMIT clause
        $limit_clause = "LIMIT $first_limit, " . POSTSPERPAGE;