I have an error in running the "php artisan serve" command in laravel , it gives the following error

 php artisan serve

PHP Fatal error: Class 'Illuminate\Foundation\Application' not found in F:\xampp\htdocs\grproject\bootstrap\app.php on line 14

Fatal error: Class 'Illuminate\Foundation\Application' not found in F:\xampp\htdocs\grproject\bootstrap\app.php on line 14

I ran the following command also, but no result, i get the above error again.

composer update