In America: Hello! or Hi! works as well. "Hello" is more polite. I would use "Hello" with someone I am meeting for the first time, or in business/formal occasions. "Hi" would most likely be used between friends or between people who have met rather briefly in the past. For example: You are walking in one direction and someone you've met before is walking in your direction. As you both pass by one another, you can say "Hi!" and continue on your way or stop and chat if you'd like. When I am passing people by (whether I know them or not), I usually smile, wave my hand a little bit, and say "Hey, how are you doing?" and continue on walking because they usually reply with "Hey! Good and you?", and I reply with "Good." Just small talk with strangers, but maybe stopping and chatting with friends if there is time to do so (if I am not busy).