server.php

<?php
session_start();

// initializing variables
$username = "";
$email    = "";
$errors = array(); 

// connect to the database
$db = mysqli_connect('loaclhost', 'username', 'password', 'table');

// REGISTER USER
if (isset($_POST['reg_user'])) {
  // receive all input values from the form
  $username = mysqli_real_escape_string($db, $_POST['username']);
  $email = mysqli_real_escape_string($db, $_POST['email']);
  $password_1 = mysqli_real_escape_string($db, $_POST['password_1']);
  $password_2 = mysqli_real_escape_string($db, $_POST['password_2']);
   $userid = mysqli_real_escape_string($db, $_POST['userid']);

  // form validation: ensure that the form is correctly filled ...
  // by adding (array_push()) corresponding error unto $errors array
  if (empty($username)) { array_push($errors, "Username is required"); }
  if (empty($email)) { array_push($errors, "Email is required"); }
  if (empty($password_1)) { array_push($errors, "Password is required"); }
  if (empty($userid)) { array_push($errors, "we need your userid");}
  if ($password_1 != $password_2) {
	array_push($errors, "The two passwords do not match");
  }

  // first check the database to make sure 
  // a user does not already exist with the same username and/or email
  $user_check_query = "SELECT * FROM usersdata WHERE username='$username' OR email='$email' LIMIT 1";
  $result = mysqli_query($db, $user_check_query);
  $user = mysqli_fetch_assoc($result);
  
  if ($user) { // if user exists
    if ($user['username'] === $username) {
      array_push($errors, "Username already exists");
    }

    if ($user['email'] === $email) {
      array_push($errors, "email already exists");
    }
  }

  // Finally, register user if there are no errors in the form
  if (count($errors) == 0) {
  	$password = md5($password_1);//encrypt the password before saving in the database

  	$query = "INSERT INTO usersdata (username, email, password, userid) 
  			  VALUES('$username', '$email', '$password', '$userid')";
  	mysqli_query($db, $query);
  	$_SESSION['username'] = $username;
  	$_SESSION['success'] = "You are now logged in";
  	header('location: index.php');
  }
}

if (isset($_POST['login_user'])) {
  $username = mysqli_real_escape_string($db, $_POST['username']);
  $password = mysqli_real_escape_string($db, $_POST['password']);

  if (empty($username)) {
    array_push($errors, "Username is required");
  }
  if (empty($password)) {
    array_push($errors, "Password is required");
  }

  if (count($errors) == 0) {
    $password = md5($password);
    $query = "SELECT * FROM usersdata WHERE username='$username' AND password='$password'";
    $results = mysqli_query($db, $query);
    if (mysqli_num_rows($results) == 1) {
      $_SESSION['username'] = $username;
      $_SESSION['success'] = "You are now logged in";
      header('location: index.php');
    }else {
      array_push($errors, "Wrong username/password combination");
    }
  }
}


if (isset($_POST['save_changes'])) {
  if (count($errors) == 0) {
    $z = $_POST['option_s'];
    $zd;
    if ($z === "Yes") {
      $zd = 1;
    }else{
      $zd = 0;
    }

      $user_check_query = "SELECT * FROM usersdata WHERE userid";
  $result = mysqli_query($db, $user_check_query);
  $user = mysqli_fetch_assoc($result);
  $userid = $user['userid'];
  

    $query = "UPDATE `Users` SET `UserTwitch`=".$_POST['tlogin']."`Stream_Text`=".$_POST['t_stream_message'].",`Remove_MSG_On_End`=".$_POST['zd']." WHERE UserID = ".$userid."";
    #UPDATE `Users` SET `UserTwitch`=smallbabytape1`Stream_Text`=лалка WHERE UserID = ".$userid.""
    $results = mysqli_query($db, $query);
    $_SESSION['success'] = "Changes has been saved!";
  }
}
?>