try

<?php

session_start();

$username = "";
$email = "";
$errors= array();

$con=mysqli_connect('localhost','root','','user');

if(isset($_POST['register'])) {
$username   = mysqli_real_escape_string($con, $_POST['username']);
$email      = mysqli_real_escape_string($con, $_POST['email']);
$password_1 = mysqli_real_escape_string($con, $_POST['password_1']);
$password_2 = mysqli_real_escape_string($con, $_POST['password_2']);



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

if (empty($email)) {
	array_push($errors, "User email is required");
}

if (empty($password_1)) {
	array_push($errors, "User Password is required");
}

if ($password_1 != $password_2) {
	array_push($errors, "Password did not match");
}


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

$password = md5($password_1);

$sql="INSERT INTO user (username, email, password) VALUES ('$username','$email','$password')";
mysqli_query($con, $sql);
$_SESSION['username'] = $username;
$_SESSION['success'] = "You are now Registered.";
header('location: confo.php');

}


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



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

if (empty($password)) {
	array_push($errors, "Valid password is required");
}

if (count($errors) == 0) {
	$password = md5($password);
	$query    = "SELECT * FROM regi WHERE username='$username' AND password='$password' ";
	$result = mysqli_query($con, $query);
	if (mysqli_num_rows($result) == 1) {
		$_SESSION['username'] = $username;
		$_SESSION['success'] = "You are now Registered.";
		header('location: confo.php');
	}else{
		array_push($errors, "The username/password did not match");
	}
 }
}





if (isset($_GET['logout'])) {
	session_destroy();
	unset($con, $_SESSION['username']);
	header('location: login.php');
}

?>