Use of undefined constant APPATH - assumed 'APPATH' - codeigniter-3

Question

I encounter this Error and i can't Fix it, Someone please help me T_T
A PHP Error was encountered
Severity: Notice
Message: Use of undefined constant APPATH - assumed 'APPATH'
Filename: controllers/Pages.php
Line Number: 4
Backtrace:
File: C:\xampp\htdocs\Project\application\controllers\Pages.php
Line: 4
Function: _error_handler
File: C:\xampp\htdocs\Project\index.php
Line: 315
Function: require_once
and this is my Code
<?php
class Pages extends CI_Controller{
public function view($page = 'home'){
if(!file_exists(APPATH.'views/pages'.$page.'php')){
show_404();
}
$data['title'] = ucfirst($page);
$this->load->view('tenplates/Header');
$this->load->view('pages/'.$page, $data);
$this->load->view('tenplates/Footer');
}
}

Answer 1

When you get a message like...
A PHP Error was encountered
Severity: Notice
Message: Use of undefined constant APPATH - assumed 'APPATH'
Filename: controllers/Pages.php
....
It means the constant, in this case APPATH is not defined. So could be a typo?
If you check out the user guide it states that it is actually APPPATH. A good way to remember it is imagining it as APPlication PATH.
3 "P"'s - not two.
So your code would then become...
<?php
class Pages extends CI_Controller{
public function view($page = 'home'){
if(!file_exists(APPPATH.'views/pages'.$page.'php')){
show_404();
}
$data['title'] = ucfirst($page);
$this->load->view('tenplates/Header');
$this->load->view('pages/'.$page, $data);
$this->load->view('tenplates/Footer');
}
}