a) combine the vector field and particle-particle interaction in an interesting way.
think, for example, about your particle particle interaction homeworks (or your vector field homeworks)
and is there any one there that you'd like to improve? Make something super interesting. No circles!
b) take a look at the flocking code, especially changing the parameters relating to flocking (see particle.cpp for the definitions of the radius and strength of the different forces). Can you make the flocking more interesting? Find the most interesting parameters (and remember, every particle doesn't have to have the same values, they can be different) and then work to use this in an interesting composition. For example, can you include other forces in addition to the flock simulation to make it more interesting? Don't forget about the other things you've learned, like the point recorder and sin/cos, etc.
c) working alone or in a group, can you design an algorithm for FASTER particle particle interaction? It must run at 30 FPS in realtime. Think about how spatial division can help, and how simple things, like sorting can be very effective. I am VERY happy to help with this.