PHP - Creating A Registration Page With Php

<?php
include 'helpfulfunctions.inc';
include 'productsdata.inc';
$user_login_file = 'login.dat';
//var_dump($_POST);
// product data for photo, name, and price.


$alluserinfo = load_users_info($user_login_file);
//validate users info
$errors = array();
if (array_key_exists('register_submit', $_POST)) {

    //check to see if username is taken
    $username_entered = $_POST['username'];
    //check to see if username already exists
    if (array_key_exists($username_entered, $alluserinfo)) {
        $errors['username']['username_exists'] = "Username already exists.";
    }
    //validate username is 4-11 characters long using only a-z A-Z 0-9
    if(preg_match("/^[0-9a-zA-z]{4,11}$/",$_POST['username']) ===0){
        $errors['username']['invalid_username']= "Invalid username. Username must be 4-11 characters long and use only letters and numbers.";
    }
    //validate password "." means any character
    //.* allows numbers 0-9 to be inserted anywhere
    //?= positive lookahead: next text must be like this and follow these rules
    // must be at least 6 characters, contain 0-9, a-z, A-Z
    $pw_entered=$_POST['password'];
    if(preg_match("/^.*(?=.{6,})(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]).*$/", $_POST["password"]) === 0){
        $errors['password']['invalid_password']="Password must be at least 6 characters and must contain at least one lower case letter, one upper case letter and one digit.";
    }
    //validate that "confirm password" matches password above
    $pw_repeat=$_POST['confirmpassword'];
    if($pw_repeat != $pw_entered){
        $errors['confirmpassword']['pw_no_match']="Passwords do not match. Try again.";
    }
    //validate email format
    $email_entered=($_POST['email']);
    if(!filter_var($email_entered, FILTER_VALIDATE_EMAIL)){
        $errors['email']['invalid_email']="Not a valid email. Please try again.";
    }
//no validation errors=>print invoice
    if (empty($errors)) {
        include 'invoice.inc';
        exit;
    }
}
//reprint if invalid entry. if no errors print invoice
?>

<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="POST">
    <h3>Please register to continue.</h3>
    <table>
        <tr>
            <td>
    *Username: 
            </td>
            <td>
    <input type="text" name="username"/>                
    <?php
    if (isset($errors['username'])) {
        print implode('<br>', $errors['username']);
    }
    ?>
            </td>
        </tr>
        <tr>
            <td>
    *Password:
            </td>
            <td>
    <input type="password" name="password"/>
    <?php
    if (isset($errors['password'])) {
        print implode('<br>', $errors['password']);
    }
    ?>
            </td>
        </tr>
        <tr>
            <td>
    *Confirm Password: 
            </td>
            <td>
    <input type="password" name="confirmpassword"/>
    <?php
    if (isset($errors['confirmpassword'])) {
        print implode('<br>', $errors['confirmpassword']);
    }
    ?>
            </td>
        </tr>
        <tr>
            <td>
    *Email: 
            </td>
            <td>
    <input type="text" name="email"/>
    <?php
    if (isset($errors['email'])) {
        print implode('<br>', $errors['email']);
    }
    ?>
            </td>
        </tr>
        <tr>
            <td>
    * required info <br>
    <input type="submit" value="Register" name="register_submit">
    <?php
    //print out hiddens with quantities
    save_hidden_qty($_POST['quantity']);
    ?>   
           
    
</form>
 </td>
        </tr>
</table>

<?php

if (!function_exists('load_users_info')) {

 function load_users_info($users_data_file) {
        $fp = fopen($users_data_file, 'r');
//read all lines of login.dat file and create user info arrays
        while (!feof($fp)) {
            $users_info_line = fgets($fp);
            $user_info_parts = explode(',', $users_info_line);
            $user_info_array = array('username' => $user_info_parts[0], 'password' => $user_info_parts[1], 'email' => $user_info_parts[2]);
            $complete_user_info_array[$user_info_array['username']] = $user_info_array;
        }

        fclose($fp);
        return $complete_user_info_array;
    }

}

// function to display products
if (!function_exists('display_products')) {

    function display_products($products_to_display, $quantities = array()) {
        global $errors;
        ?>
        <table border="1">
            <tbody>
                <tr>
                    <td style="text-align: center;"><b><big>Product</big></b></td>
                    <td style="text-align: center;"><b><big>Brand</big></b></td>
                    <td style="text-align: center;"><b><big>Price(each)</big></b></td>
                    <td style="text-align: center;"><b><big>Quantity Desired</big></b></td>
                </tr>
                <?php

                // quantities are 0 unless already inputted, if quantities previously were inputted, return the values. 
                // input boxes
                for ($i = 0; $i < count($products_to_display); $i++) {
                    if (empty($quantities)) {
                        $qty = isset($_POST['quantity'][$i]) ? $_POST['quantity'][$i] : 0;
                        $qty_str = "<input type=text size=3 maxlength=3 name='quantity[$i]' value='$qty'>";
                        if (isset($errors['quantity'][$i])) {
                            $qty_str .= "<span style='font-style:italic;font-size:8px;color:red;'>{$errors['quantity'][$i]}</span>";
                        }
                    } else {
                        $qty_str = $quantities[$i];
                    }
                    // loop to print out table of photo of board, name of the brand, price, and quantity selected
                    printf('
                <tr>
                    <td><img alt="Small" id="lightboxImage"
                             style="width: 119px; height: 88px; bgcolor="#cccccc;"
                             src="http://imgur.com/%s"
                             height="300" width="300"></td>
                    <td style="text-align: center;">%s</td> 
                    <td style="text-align: center;">$%.2f</td>
                    <td style="text-align: center;">' . $qty_str . '</td>
                </tr>
                        ', $products_to_display[$i]['item'], $products_to_display[$i]['board'], $products_to_display[$i]['price']);
                }
                ?>
                <tr><td colspan="4" style="text-align: right; border: none">
                        <input type="submit" value="Purchase"></td></tr>

            </tbody>
        </table>
    <?php

    }

}

if (!function_exists('save_hidden_qty')) {
    function save_hidden_qty($the_quantities){
        foreach ($the_quantities as $key=>$value){
            print "<input type='hidden' name='quantity[$key]' value='$value'>\n";
        }
    }
}

?> 

<iframe src="SMQ.php" scrolling="yes" width="950" height="800"></iframe>

SELECT * FROM `SMQSQL` WHERE `Scott` = '226' ORDER BY `LINEID` ASC 

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Example of Google Spreadsheet Data Visualisation</title>
</head>

<body>

<form id="form1" method="post" action ="<?php echo $_SERVER['PHP_SELF']; ?>"> <label>
<input id="search" name="search" type="text" />
</label>
<label>
<input id="Scott #" name="Scott #" type="submit" value="Scott #" />
</label>

<img src="loading.gif" width="16" height="11" />
</form>
<p>
<?php
$search= $_REQUEST['search'];
if ($search > ''){ $search = $search;} else { $search = '';}
?>
<script type="text/javascript" src="http://www.google.com/jsapi"></script>
<script type="text/javascript">
google.load('visualization', '1', {packages: ['table']});
</script>
<script type="text/javascript">
var visualization;
function drawVisualization() {

var query = new google.visualization.Query(
'https://docs.google.com/spreadsheet/ccc?key=0AronCwm9QPefdGpIUllscGgtLUJod2pOazc0bjU0cUE&usp=sharing');

query.setQuery('SELECT A, B, C, D, E, F, G, H, I, J, K, L, M, N, O ,P ,Q ,R ,S ,T WHERE (A) LIKE ("<?php echo $search; ?>") order by A asc label A "Scott #", B "Den", C "Color", D "Cond", E "40", F "60", G "70", H "70J", I "75", J "75J", K "80", L "80J", M "85", N "85J", O "90", P "90J", Q "95", R "95J", S "98", T "98J"');
query.send(handleQueryResponse);
}

function handleQueryResponse(response) {
if (response.isError()) {
alert('Error in query: ' + response.getMessage() + '' + response.getDetailedMessage());
return;
}

var data = response.getDataTable();

    visualization = new google.visualization.Table(document.getElementById('table'));
    visualization.draw(data, { page: 'enable', page: 16, pageSize: 16, legend: 'bottom'});
}
google.setOnLoadCallback(drawVisualization);
</script>

 <div id="table"></div>

</div>

</body>
</html>

I've started a to-do app, and everything works fine. Every user has his own unique to-do items that he can add. The only issue is that when I log-in with a user, ALL the items of all users are displayed when I'm redirect to my main page. I want to make it as so every user has his own page where only the to-do items he has created are visible, not every item from every user. I'm a total beginner with PHP so I'm sorry if this is a stupid question.

This is my todomain.php code

<?php
require 'db_conn.php';
require 'config.php';
session_start(); 
   
// If the session variable is empty, this  
// means the user is yet to login 
// User will be sent to 'login.php' page 
// to allow the user to login 
if (!isset($_SESSION['id'])) { 
    $_SESSION['msg'] = "You have to log in first"; 
    header('location: login.php'); 
} 
   
// Logout button will destroy the session, and 
// will unset the session variables 
// User will be headed to 'login.php' 
// after loggin out 
if (isset($_GET['logout'])) { 
    session_destroy(); 
    unset($_SESSION['id']); 
    header("location: login.php"); 
} 


?>

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset= "UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="IE=edge"> 
<link rel="stylesheet" href="css/bootstrap-grid.min.css">
<link rel="stylesheet" href="css/bootstrap.min.css">
<link rel="stylesheet" href="style.css">
<a href="index.php?logout='1'" style="color: black;"> 
                    Click here to Logout 
                </a> 
 <?php if (isset($_SESSION['success'])) : ?> 
            <div class="error success" > 
                <h3> 
                    <?php
                        echo $_SESSION['success'];  
                        unset($_SESSION['success']); 
                        echo $_SESSION["username"]
                    ?> 
                </h3> 
            </div> 
        <?php endif ?> 

<title>TODO App</title>
<script src="https://kit.fontawesome.com/d72928d9b9.js" crossorigin="anonymous"></script>
</head>
<body>
    <div class="container m-5 p-2 rounded mx-auto bg-light shadow">
    <!-- App title section -->
    <div class="row m-1 p-4">
        <div class="col">
            <div class="p-1 h1 text-primary text-center mx-auto display-inline-block">
                <i class="fa fa-check bg-primary text-white rounded p-2"></i>
                <u>My Todo-s</u>
            </div>
        </div>
    </div>
    <!-- Create todo section -->
  <form action="app/add.php" method="POST" autocomplete="off">
    <div class="row m-1 p-3">
        <div class="col col-11 mx-auto">
            
            <div class="row bg-white rounded shadow-sm p-2 add-todo-wrapper align-items-center justify-content-center">
                
                <div class="col">
                    <input class="form-control form-control-lg border-0 add-todo-input bg-transparent rounded" type="text" name="title" placeholder="Add new ..">
                </div>
                <div class="col-auto m-0 px-2 d-flex align-items-center">
                    <label class="text-secondary my-2 p-0 px-1 view-opt-label due-date-label d-none">Due date not set</label>
                    <i class="fa fa-calendar my-2 px-1 text-primary btn due-date-button" data-toggle="tooltip" data-placement="bottom" title="Set a Due date"></i>
                    <i class="fa fa-calendar-times-o my-2 px-1 text-danger btn clear-due-date-button d-none" data-toggle="tooltip" data-placement="bottom" title="Clear Due date"></i>
                </div>
                
                <div class="col-auto px-0 mx-0 mr-2">
                    
                    <button type="submit" class="btn btn-primary">Add</button>
                    
                    
                </div>
             
            </div>

            
        </div>
    </div>
    </form>

     
          <?php
            $todos=$conn->query("SELECT * FROM  todos ORDER BY id ASC");
          ?>

 
  <div class="row mx-1 px-5 pb-3 w-80">
        <div class="col mx-auto">

           <?php
           while($todo=$todos->fetch(PDO::FETCH_ASSOC)){ ?>
            <!-- Todo Item 1 -->

            
            <div class="row px-3 align-items-center todo-item rounded">

                <?php if($todo['checked']){ ?>
                
                <input type="checkbox" class="check-box" data-todo-id="<?php echo $todo['id'];?>" checked />
            <h2 class="checked"><?php echo $todo['title'] ?> </h2>
            <div class="col-auto m-1 p-0 todo-actions">
                    <div class="row d-flex align-items-center justify-content-end">
              
            </div>
          </div>
        
             

                      
            <?php } else{ ?>
                <input type="checkbox" class="check-box" data-todo-id="<?php echo $todo['id'];?>"/>
                 <h2><?php echo $todo['title'] ?></h2>
                   
                          

            <?php } ?>

                <div class="col-auto m-1 p-0 d-flex align-items-center">


                    <h2 class="m-0 p-0">
                        <i class="fa fa-square-o text-primary btn m-0 p-0 d-none" data-toggle="tooltip" data-placement="bottom" title="Mark as complete"></i>
                        
                    </h2>
                </div>
               
                
             
                <div class="col-auto m-1 p-0 todo-actions">
                    <div class="row d-flex align-items-center justify-content-end">

                        <h5 class="m-0 p-0 px-2">
                            <i class="fa fa-pencil text-info btn m-0 p-0" data-toggle="tooltip" data-placement="bottom" title="Edit todo"></i>
                        </h5>
                        <h5 class="m-0 p-0 px-2">
                          
                             
                        <i class="remove-to-do fa fa-trash-o text-danger btn m-0 p-0" data-toggle="tooltip" data-placement="bottom" title="Delete todo" id="<?php echo $todo['id']; ?>"></i>
                      </h5> 
                    </div>
                    <div class="row todo-created-info">
                        <div class="col-auto d-flex align-items-center pr-2">
                            <i class="fa fa-info-circle my-2 px-2 text-black-50 btn" data-toggle="tooltip" data-placement="bottom" title="" data-original-title="Created date"></i>
                            <label class="date-label my-2 text-black-50"><?php echo $todo['date_time'] ?></label>
                        </div>
                    </div>
                </div>
            </div>
        
        <?php } ?>

    

</div>


 <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js" integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49" crossorigin="anonymous"></script>
    <script src="js/bootstrap.bundle.min.js"></script>
    <script src="js/myjs.js" ></script>
    <script src="js/jquery-3.3.1.min.js"></script>

    <script>
        $(document).ready(function(){

          $(".remove-to-do").click(function(e){
                const id = $(this).attr('id');
                 $.post('app/remove.php', 
                      {
                          id: id
                      },
                      (data) => {
                         if(data){
                            $(this).parent().parent().parent().parent().hide(300);
                         }
                      }

                );
                
               
            });
          


            $(".check-box").click(function(e){
                const id = $(this).attr('data-todo-id');
                
                $.post('app/checking.php', 
                      {
                          id: id
                      },
                      (data) => {
                         if(data!='error'){
                            const h2= $(this).next();
                            if(data === '1'){
                                h2.removeClass('checked');
                            }else{
                                h2.addclass('checked');
                            }
                         }
                      }

                );
            });
        });
    </script>


</body>
</html>