Looks like you were inspired by Resident Evil 4's inventory system.
Recent community posts
I've noticed some errors in your examples. Page 17 in the coding and text where it says "bat_x=bat_x+3" in the function move_bat(). In page 40 under the same function move_bat() it changed to "bat_x=bat_x+bat_speed" without any explanation. Also on page 36 it says at the top "detect_collision" even though in previous examples say "check_collision".