I don't have a lock on my door...and there is no way to lock it short of getting a 5 foot long piece of wood and Midieval times castle locking it (like...rest the wood across the door) cause the only door that would fit the frame that is on my room when I moved in was closet doors (like the accordian doors) haha
If I don't want somebody to come in my room. I turn my skateboard upside down and push it under the door.