Here is the easy way to make a character jump.
Keep track of a jump velocity.
Whenever the player jumpes, set jump velocity to some number (whatever number will look good in your game). This determines how much force the player jumps off the ground with.
As your character is jumping, between each frame, decrease jump velocity by another number-- the higher this other number, the lower your character will be able to jump. This other number will be like gravity.
i.e.
jumpVelocity = 20;while ( playingGame){ playerY += jumpVelocity; jumpVelocity -= 2 if ( playerHitsThefloor) jumpV = 0;}
You can make this more complicated, by keeping track of gravity and the players jumping power separately, or doing other nifty things, but essentially you just need to make the player go up and come back down again. :)
i.e.
playerY += jumpVelocity; playerY -= gravity; jumpVelocity = jumpVelocity / 2;
It's all about what looks good, unless you're doing a simulation of some sort of course.
Best of luck,
Will