This is my web application codes for a registration form( login codes, error codes, index codes and server codes for my web application)

When i log in with already registered details, it doesnt open to the next page(logged in successfully)

I will be very happy if you identify the error for me

Use this codes and identify the error for me to login with already registered details

Nb: moreover, write a nice designed css code for this codes for nice presentation

REGISTRATION.PHP

Registration System

REGISTER

 

First Name

Last Name

Email

School ID

PIN :

    Confirm PIN :

Already have account? Log In

LOGIN.PHP

Registration system

LOG IN

School ID

PIN :

Not a user? Register Here

ERROR.PHP

0) : ?>

SERVER.PHP

session_start();

// initializing variables

$First_name = "";

$Last_name = "";

$Email    = "";

$School_ID    = "";

$PIN    = "";

$msg = "";

$errors = array(); 

// connect to the database

$db = mysqli_connect('localhost', 'root', '', 'student') or die('Could not connect to database');

//If tthe register button is clicked 

if (isset ($_POST ['reg_student'])){

  // REGISTER student

  // receive all input values from the form

  $First_name = mysqli_real_escape_string($db, $_POST['First_name']);

  $Last_name = mysqli_real_escape_string($db, $_POST['Last_name']);

  $Email = mysqli_real_escape_string($db, $_POST['Email']);

  $School_ID = mysqli_real_escape_string($db, $_POST['School_ID']);

  $PIN_1 = mysqli_real_escape_string($db, $_POST['PIN_1']);

  $PIN_2 = mysqli_real_escape_string($db, $_POST['PIN_2']);

  // form validation: ensure that the form is correctly filled ...

  // by adding (array_push()) corresponding error unto $errors array

  if (empty($First_name)) {

    array_push($errors, "First name is required");

  }

  if (empty($Last_name)) {

    array_push($errors, "Last Name is required");

  }

  if (empty($School_ID)) {

    array_push($errors, "School ID is required");

  }

  if (empty($PIN_1)) {

    array_push($errors, "PIN is required");

  }

  if ($PIN_1 != $PIN_2){

    array_push($errors, "PIN do not match");

  }

  

  // first check the database to make sure 

  // a student does not already exist with the same school ID and/or email and/or pin

  $registration_form_check_query = "SELECT * FROM registration_form  WHERE School_ID='$School_ID' OR Email='$Email' OR PIN='$PIN' LIMIT 1";

  $results = mysqli_query ($db, $registration_form_check_query);

  $registration_form = mysqli_fetch_assoc($results);

  

  if ($registration_form) { // if student exists

    if ($registration_form ['School_ID'] === $School_ID) {

      array_push($errors, "School ID already exists");

    }

    if ($registration_form ['Email'] === $Email) {

      array_push($errors, "Email already exists");

    }

        

        if ($registration_form ['PIN'] === $PIN) {

      array_push($errors, "PIN already exists");

    }

        

  }

  // Finally, register student if there are no errors in the form

  if (count($errors) == 0) {

        $PIN = md5($PIN_1); //This will encrypt the pin

        $sql = "INSERT INTO registration_form (First_name, last_name, Email, School_ID, PIN) 

                          VALUES('$First_name', '$Last_name', '$Email', '$School_ID', '$PIN')";

      $sql =mysqli_query($db, $sql);

        

        if ($sql) {

                $msg = "Registration successfully completed";

        

        header('location: index.php');

  }

  

}

// USER LOGIN

if(isset($_POST['Login_user'])){

  $School_ID = mysql_real_escape_string($db, $_POST['School_ID']);

  $PIN= mysql_real_escape_string($db, $_POST['PIN']);

if(empty($School_ID)){

  array_push($errors, "School ID is required");

}

if(empty($PIN)){

array_push($errors, "PIN is required");

}

if(count($errors) == 0){

  $PIN = mds($PIN);

  $sql = "SELECT * FROM registration_form WHERE School_ID = '$School_ID' AND PIN = '$PIN' ";

$results = mysql_query($db, $sql);

if(mysqli_num_rows($results)){

  $_SESSION['School_ID'] = $School_ID;

$_SESSION['SUCCESS'] = "LOGGED IN SUCCESSFULLY";

header('location: index.php');

}

else{

  array_push($errors, "WRONG School_ID/ PIN. PLEASE TRY AGAIN.");

}

}

}

INDEX.PHP

session_start();

if(isset($_SESSION['School_ID'])){

$_SESSION['msg'] = "You must log in first to view this page ";

header("location : login.php");

}

if(isset($_GET['Logout'])){

session_destroy();

unset($_SESSION['School_ID']);

header("location : login.php");

}

?>

<b>HOME PAGE</b>

This is the homepage

if(isset($_SESSION['success'])) : ?>

echo $_SESSION['success'];

unset($_SESSION['success']);

?>

If the user logs in, print information about him

Welcome

 }