Negative Numbers and Modulo

What is $-7 \bmod 3$? Mathematically, it should be $2$ (because $-7 = 3 \times (-3) + 2$). But different programming languages give different answers.

Python gives $2$. C++ and Java give $-1$. This happens because they use different definitions of the remainder operation for negative numbers.

To get a positive result in any language, use: $(a \bmod m + m) \bmod m$. This formula always gives a value between $0$ and $m - 1$.