Please describe your problem in the post, it took me a while to figure that that it was hidden in the code via comments…
-100 is less then the current balance of
200, so it gets subtracted,
200 - -100 is equivalent to
200 + (-1 * -100) which is
200 + 100, so
300 is the correct result.
Sorry about that. My bad, I’ve figured out the solution.