correct way to find the result of modulo

Question

As We all know, modulo operation finds the remainder of division of one number by another.

I'm strruggling to figure out the correct way to get value of modulo.

a mod b = c

It's easy to find c if a >= 0. But, if a < 0, it's confusing me.

One day, I read in my lecturer notes if -75 mod 26 = 3.

Then, I create a simple program in java to find the result of -75 mod 26. The program compiles and prints result: -23.

So, what is the right way to find c if a < 0?

Belows is code I've tried:

public class modulo {
    public static void main(String [] args){
        int divide = -75;  

        int val = divide % 26; 

        System.out.println(divide+" % 26 = "+ val);

    }
}

Could you not just do mod abs(number) and then re make it negative — Jeef, Apr 01 '14 at 12:45

score 0 · Answer 1 · answered Apr 01 '14 at 12:51

0

Why won't you get absolute value from both before division?

public class modulo {
    public static void main(String [] args){
        int divide = -75;  
        int val = Math.abs(divide) % Math.abs(26); 
        System.out.println(divide+" % 26 = "+ val);
    }
}

...or simply get abs value from the result (with rounding)?

Math.round( result );

answered Apr 01 '14 at 12:51

Miron Balcerzak

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Simply rounding the result will yield wrong result. – assylias Apr 01 '14 at 14:46
I just proposed the solution. For proper rounding he can search for proper implementation (or write his own) – Miron Balcerzak Apr 01 '14 at 15:01
What I'm saying is that `abs(a % b) != abs(a) % abs(b)`. The latter is mathematically correct but the former isn't. – assylias Apr 01 '14 at 15:28

correct way to find the result of modulo

1 Answers1