If you want to allow the user to choose between one of the various different games you have, you're going to need to add additional game states anyway. You can simply make you level-loading conditional on both which game is being played and which level to load. It's hard to explain without seeing an example of how you're doing your games.

You might also want to consider moving your setup code for your games into a separate reset function. Instead of:

1. int x,y;
2. void setup(){
3.   size(...);
4.   x = 20;
5.   y = 30;
6. }
7. // ...

@tfguy44 : so thats what my doubt is. So i need to have different reset functions depending on the number of levels, right?