what would u do if your friend gets credited for your work?

Ok, here's what happened.

Last week, my friend who takes art have to create some kind of art related to shapes. I'm not exactly sure about the criteria. He asked me about it, and I suggested him to write a computer program that have shapes floating around. He's not really good at computer science although he takes it too. I then ended up writing the program for him. It was quite easy, took me only 30 min or so. The program is not that great, it just have 10 rectangle, trapezoid, parallelogram, diamonds with different color, moving at different speed, and in different motion. I basically write a process for 1 shape, and then copy/paste the whole process except change the drawing to a different shape. and call each process 10 times. The speed and motion is at random, which is why each shape have different speed and motion.
Today when he handed in, the teacher is impressed about how much work he put into this art piece (she obviously knows nothing about computer science cause it's such a easy program to write). She said she's going to display the work at a local art museum. Now... the "artwork" is going to be displayed in an art museum with my friend's name on it.

Should i do something about it? but I don't want to screw over my friend...

not sure if this is appropriate - but i suggest perhaps that you speak to the teacher in private and explain your situation, making sure to add that you do not want your friend to know. i mean it is not illegal to help your friends with assignments and such! his teacher will hopefully understand and quietly decide not to display it.

on the other hand, your friend will still have to field the questions about how he thought of it etc. he might himself feel guilty about it, and take the initiative to explain to the teacher that it is actually not all his work.