I am new in Laravel and using laravel version 5.2.
I created a controller and request named as ArticlesController and CreateArticleRequest
This happens because the file below is not updated in the composer update process, so doesn't have the mapWebRoutes method implemented.
mapWebRoutes
app/Providers/RouteServiceProvider.php
Copy this file over from a fresh install and it will work. Better, follow the upgrade path on the docs.