send.php

<?PHP

$message = "";

//initializing connection variables 

$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";



// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 


//user's information
$firstname  = filter_var(mysqli_real_escape_string($conn, $_POST['firstname']));
$lastname = filter_var(mysqli_real_escape_string($conn, $_POST['lastname']));
$email = filter_var(mysqli_real_escape_string($conn, $_POST['email']));

//code formation
$generator = "1234567890";

//shuffling generator and specifying 6-digit code 
$code = substr(str_shuffle($generator), 0, 6);

$sql = "INSERT INTO users (firstname, lastname, email, code) VALUES ('$firstname', '$lastname', '$email', '$code')";


if ($conn->query($sql) === TRUE) {
    
    $message =  "Check your inbox for your code !!!";
    //storing code for only 10 minutes (Setting cookie)
    
    setcookie("code", $code, time() +(10*60*60));
    
    //redirecting user to validation page
    header('location: validate.php');
} else {
    $message =  "Error: " . $sql . "<br>" . $conn->error;
}

$conn->close();
?>