**my functions.php file**
                                                 <?php
                                                 function confirmquery( $result ){
                                                     global $db;
                                                     if(!$result){
                                                        die("OUERY FAILED .".mysqli_error($db));
                                                      }
                                                }

                                                function redirect($location){
                                                  return header("Location:". $location);
                                                }

                                                function is_admin($username = ''){
                                                    global $db;
                                                    $sql = "SELECT user_role FROM users WHERE username = '$username'";
                                                    $result = mysqli_query($db, $sql);
                                                    confirmquery( $result );
                                                 $row = mysqli_fetch_array($result);
                                                     if ($row['user_role'] == 'admin') {
                                                       return true;
                                                     }else {
                                                       return false;
                                                     }
                                                }

                                                function username_exists($username = ''){
                                                    global $db;
                                                    $sql = "SELECT 'username' FROM users WHERE 'username' = '$username'";
                                                    $result = mysqli_query($db, $sql);
                                                    confirmquery( $result );

                                                      if (mysqli_num_rows($result) > 0) {
                                                        return true;
                                                      }else {
                                                        return false;
                                                      }
                                                }

                                                function email_exists($user_email = ''){
                                                    global $db;
                                                    $sql = "SELECT 'user_email' FROM users WHERE 'user_email' = '$user_email'";
                                                    $result = mysqli_query($db, $sql);
                                                    confirmquery( $result );

                                                     if (mysqli_num_rows($result) > 0) {
                                                       return true;
                                                     }else {
                                                       return false;
                                                     }
                                                }

                                                function recordCount($table){
                                                    global $db;
                                                  $sql    =" SELECT * FROM ".$table;
                                                  $result = mysqli_query($db, $sql);
                                                  return  mysqli_num_rows($result);

                                                }

                                                function register_user($username,$user_email,$user_password){
                                                  global $db;

                                                    $username     =mysqli_real_escape_string($db,$username);
                                                    $user_email   =mysqli_real_escape_string($db,$user_email);
                                                    $user_password=mysqli_real_escape_string($db,$user_password);

                                                    $user_password = password_hash($user_password, PASSWORD_BCRYPT, array('COST' => 12 ));

                                                    $sql="INSERT INTO `users`
                                                              SET

                                                            `username`         ='{$username}',
                                                            `user_email`       ='{$user_email}',
                                                            `user_password`    ='{$user_password}',
                                                            `user_role`        ='user'";

                                                      $result = mysqli_query($db, $sql);
                                                      confirmquery( $result );

                                                }

                                                function login_user($user_email, $user_password){
                                                      global $db;
                                                      $user_email    =trim($user_email);
                                                      $user_password =trim($user_password);

                                                      $user_email = mysqli_real_escape_string($db,$user_email);
                                                      $user_password = mysqli_real_escape_string($db,$user_password);

                                                 $sql = "SELECT * FROM `users` WHERE user_email='{$user_email}'";
                                                 $result = mysqli_query($db, $sql);
                                                     if(!$result){
                                                         die("OUERY FAILED .".mysqli_error($db));
                                                       }

                                                  while($row = mysqli_fetch_array($result)){
                                                     $db_user_id = $row['user_id'];
                                                     $db_username = $row['username'];
                                                     $db_user_email = $row['user_email'];
                                                     $db_user_password = $row['user_password'];
                                                     $db_user_firstname = $row['user_firstname'];
                                                     $db_user_lastname = $row['user_lastname'];
                                                     $db_user_role= $row['user_role'];
                                                     }
                                                    // $user_password = crypt($user_password,$db_user_password);

                                                if (password_verify($user_password, $db_user_password)) {
                                                $_SESSION['db_username']       = $db_username;
                                                $_SESSION['db_user_firstname'] = $db_user_firstname;
                                                $_SESSION['db_user_lastname']  = $db_user_lastname;
                                                $_SESSION['db_user_role']      = $db_user_role;

                                                  redirect("/gms/index.php");
                                                }

                                                }

                                                 ?>

                             **My registration.php file**     

                        <?php   include "includes/connect.php"; ?>
                        <?php  include "includes/header.php"; ?>
                        <?php  include "./admin/functions.php"; ?>

                         <?php
                             if ($_SERVER['REQUEST_METHOD'] == "POST") {
                              $username      =trim($_POST['username']);
                              $user_email    =trim($_POST['email']);
                              $user_password =trim($_POST['password']);

                              $error = [
                                'username' => '',
                                'email' => '',
                                'password' => ''
                              ];

                              if(strlen($username) < 4){
                                $error['username'] = 'Username needs to be longer';
                              }

                              if($username == ''){
                                $error['username'] = 'Username cannot be empty';
                              }

                              if(username_exists($username)){
                                $error['username'] = 'Username already exists';
                              }

                              if($user_email == ''){
                                $error['email'] = 'Email cannot be empty';
                              }

                              if(email_exists($user_email)){
                                $error['email'] = 'Email already exists, <a href = "index.php">Please login</a>';
                              }

                              if($user_password == ''){
                                $error['password'] = 'Password cannot be empty';
                              }

                              foreach ($error as $key => $value) {
                                if(empty($value)){
                                  unset($error[$key]);
                                  }
                                }

                                if(empty($error)){
                                  register_user($username, $user_email, $user_password);
                                  login_user($user_email, $user_password );
                                }

                            }

                          ?>

                            <!-- Navigation -->

                            <?php  include "includes/navigation.php"; ?>

                            <!-- Page Content -->
                            <div class="container">

                        <section id="login">
                            <div class="container">
                                <div class="row">
                                    <div class="col-xs-6 col-xs-offset-3">
                                        <div class="form-wrap">
                                        <h1>Register</h1>
                                            <form role="form" action="registration.php" method="post" id="login-form" autocomplete="oFF">

                                                <div class="form-group">
                                                    <label for="username" class="sr-only">username</label>
                                                    <input type="text" name="username" id="username" class="form-control" placeholder="Enter Desired Username"
                                                      autocomplete="on"
                                                      value = "<?php echo isset($username) ? $username : '' ?>"  >
                                                      <p><?php echo isset($error['username']) ? $error['username'] : '' ?></p>

                                                </div>
                                                 <div class="form-group">
                                                    <label for="email" class="sr-only">Email</label>
                                                    <input type="email" name="email" id="email" class="form-control" placeholder="somebody@example.com"

                                                    value = "<?php echo isset($user_email) ? $user_email : '' ?>">
                                                    <p><?php echo isset($error['email']) ? $error['email'] : '' ?></p>

                                                </div>
                                                 <div class="form-group">
                                                    <label for="password" class="sr-only">Password</label>
                                                    <input type="password" name="password" id="key" class="form-control" placeholder="Password">

                                                    <p><?php echo isset($error['password']) ? $error['password'] : '' ?></p>

                                                </div>

                                                <input type="submit" name="register" id="btn-login" class="btn btn-custom btn-lg btn-block" value="Register">
                                            </form>

                                        </div>
                                    </div> <!-- /.col-xs-12 -->
                                </div> <!-- /.row -->
                            </div> <!-- /.container -->
                        </section>

                                <hr>

                        <?php include "includes/footer.php";?>
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