Hi there,
well dangerous is relative. When you go avoid the beach at Copacabana in the evening hours (lot's of muggings there). Otherwise, you shouldn't have any problems in Rio if you apply common sense.
Cities like St. Louis, New Orleans, and Detroit are more dangerous than Rio de Janeiro.
P.S. When you go, then go to the "Lapa" street festival every Friday night until early Saturday morning. It's really great
No, just be careful
no man its chilled! have a good one