[RESOLVED] Drawing Circles

For my CompSc 101 class I'm assigned the completely abitrary and retarded assignment of creating a ppm image with a couple cirlces in it. If you don't know what a ppm is, it's a type of image file that is created by a single line of successive characters that each define the color of the pixel. There are no rows or spaces, even if the picture is a box the way the image is created in C is the same, pixel after pixel.

So, for simple objects like colored squares and checkerboards this is easy. Instead, our teacher wants us to draw a circle, and multiple ones at that. What this has to do with computer science I don't know, this is more math than anything else. Either way I was wondering if anyone could point me in the right direction or give me some advice to get me started. I haven't tried coding yet because honestly I can't find any point of attack. The hardest part is because the circle will be drawn row by row inside a square box, there's no skipping around and all the blank spaces must be filled. I would appreciate any advice on where to start for this project.