rotating a cube around origin

I'm working on a yahtzee program, and I want to make a neat animation of rolling dice. I've gotten as far as rendering the wireframe cube, and I've made some rotation functions for each axis that look something like this:

Code:

---

th = atan(y / x);
if ((x < 0 && y < 0) || (x < 0 && y > 0)) // -1/1 = 1/-1, correct for atan()
  th += pi / 2;
th += pi / 20;
x = size * cos(th);
y = size * sin(th);

---

here's the part that stumps me, these functions work fine by themselves, but when I run them more than one at once I get weird (noncube) results. Does anybody have any ideas as to why this might be happening?

no not without more code,

this site explains using matrices to do rotation around an arbitrary axis, which is probably easier.

http://www.geocities.com/SiliconVall.../matrices.html