c modulus operator

Question

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

Answer 1

The % operator gives the remainder for integer division, so that (a / b) * b + (a % b) is always equal to a (if a / b is representable; in two's complement notation the most negative integer divided by -1 is not representable).

This means that the behaviour of % is coupled to that of /. Prior to C99 the rounding direction for negative operands was implementation-defined, which meant that the result of % for negative operands was also implementation-defined. In C99 the rounding for / is towards zero (decimals are simply truncated), which also fixes the behaviour of % in C99.