I used tigcc to write a program that can draw the root locus (https://en.m.wikipedia.org/wiki/Root_locus). I had a version that ran in ti basic at first, but it was too slow because it had to solve a polynomial (order 3 or 4) per pixel. It was my way of cheating, because the calculator was allowed in most exams. I considered it not quite cheating, because I figured being able to code the solution should also count.

I also coded up ti basic programs that instead of just spewing out the solution to some types of maths problems also gave the steps. That saved a lot of time in maths exams so that I had more time for the problems that required more thought.