How on earth would you get 4 out of 9 remainder 5? If you want a positive remainder, it would be 1.
You should read about the conventions behind the % operator. It is defined as a “Euclidean” operator, which means that multiplying back and adding the remainder gives the original dividend. If you try -9 % -5 and get a remainder of 1, then that is not “Euclidean”; if you multiply back, you will get -4.