Is there any way to write “mod 31” without modulus/division operators?

Question

Getting the modulus of a number can be easily done without the modulus operator or divisions, if your operand is a power of 2. In that case, the following formula holds:

Answer 1

You could use successive addition / subtraction. There is no other trick since 31 is a prime number to see what the modulus of a number N is mod 31 you will have to divide and find the remainder.

int mode(int number, int modulus) {
    int result = number;

    if (number >= 0) {
         while(result > modulus) { result = result - modulus;}
    } else {
         while (result < 0) { result = result + modulus;)
    }
}