Getting started in Game Programming -- a simple algorithm

Have it set the character''s vertical velocity to -10 (go up 10 pixels at a time), make a gravity value like 5 or something and add that to the velocity every frame. That way, when you jump, you go up really fast, then the gravity pulls you back down so your velocity will be like -10, -5, 0, 5, 10, 15, etc. until you hit the ground. The 5 and 10 are just random numbers for the demonstration, so you''ll have to experiment around until you get the speed right.
Oh, and you should use floats (or fixed point cause it''s faster) so you can have sub-pixel movement (else you''ll only be able to move in 8 directions).

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-Deku-chan

DK Art (my site, which has little programming-related stuff on it, but you should go anyway^_^)

btw, deku''s method will make a parabola.