Register style programming is when a coder of a high level language treats variables as if they were programming in assembly with registers.

room = RoomDAO.findLivingRoom  
if (room <> nil)  
  house.add(room)  
room = RoomDAO.findKitchen  
if (room <> nil)  
  house.add(room)

Reusing variables with register style programming has several problems:

1. It unnecessarily increases the lifetime of a variable thus making it harder for code readers to track the variables state.
2. It makes the code less self-documenting forcing the reader to track a variable through the program to determine which meaning the variable has at one time.

Instead, variables should have only a single semantic meaning throughout their lifetime.

livingRoom = RoomDAO.findLivingRoom  
if (livingRoom <> nil)  
  house.add(livingRoom)  
kitchen = RoomDAO.findKitchen  
if (kitchen <> nil)  
  house.add(kitchen)