He could be very flirty. As in he will come up and touch you much more then usual. He may also try to talk to you differently. In a more of a flirty fasion.
Ask him to go with you to the party
if he still wants to hang out with you Eg: the park, the movies, a party, anywhere.
He will tell you he likes you or will ask you to do something with him (go for coffee, see a movie, go to a party together).
when he says he likes you.
iam in love with this guy but i do not know if he likes me or some other girl
If a guy likes you but you don't know him he may look at you or walk by you whenever possible.
http://www.wikihow.com/Know-if-a-Guy-Likes-You
Not sure how you expect someone to magically know something.
It is ok to like a guy after you know he likes you. That is perfectly normal and a part of life.
You ask the guy.
don't
When he has a penis.