How to make the mod of a negative number to be positive?

Question

Basically, I need (-3) % 5 to be \"2\" instead of \"-3\". Python produces \"2\", but C++ produces \"-3\". Not sure how to produce \"2\" in C++. Thanks!

Answer 1

You can add some multiple of 5 to the negative number first, to convert it to a positive number with the same value mod 5.

You can do that by taking the absolute of the negative number, adding whatever is needed to round it up to the next multiple of 5, and then add it to your negative number, and that should already be a number between 0 and 4.

Alternatively, simply do something like:

num = -2;
mod = 5;
if ( num < 0 ) {
    result = mod - (abs(num) % mod);
}

and it'll work (explanation: mathemagic)