C++/SFML - Shooter game test

I’ve been using SFML for over two years, and I’ve been writing some sort of “engine“ for a year and a half. Normally people would advice against writing an engine and I agree, but in my case, as I had no idea of the game I wanted to make exactly, but rather just had vague concepts, I decided to write a code that would work regardless of the type of game instead of waiting for an idea with my arms crossed. So, with that said, in August 2014 I decided to use the year-old “engine“ to make something playable,