c modulus operator

Question

what happens when you use negative operators with %. example -3%2 or 3%-2

Answer 1

In C99 a % b has the sign of a, pretty much like fmod in math.h. This is often what you want :

unsigned mod10(int a)
{
    int b = a % 10;
    return b < 0 ? b + 10 : b;
}