How does the modulus operator work?

Question

Let's say that I need to format the output of an array to display a fixed number of elements per line. How do I go about doing that using modulus operation?

Using C++, the code below works for displaying 6 elements per line but I have no idea how and why it works?

for ( count = 0 ; count < size ; count++)
{
    cout << somearray[count];
    if( count % 6 == 5) cout << endl;
}

What if I want to display 5 elements per line? How do i find the exact expression needed?

Please note that the name of the operation is **modulo operation**. The term **modulus** is the role given to `b` in `a % b`. https://en.wikipedia.org/wiki/Modulo_operation — parml, Sep 02 '19 at 08:20

score 43 · Answer 1 · answered Sep 23 '12 at 22:58

in C++ expression a % b returns remainder of division of a by b (if they are positive. For negative numbers sign of result is implementation defined). For example:

5 % 2 = 1
13 % 5 = 3

With this knowledge we can try to understand your code. Condition count % 6 == 5 means that newline will be written when remainder of division count by 6 is five. How often does that happen? Exactly 6 lines apart (excercise : write numbers 1..30 and underline the ones that satisfy this condition), starting at 6-th line (count = 5).

To get desired behaviour from your code, you should change condition to count % 5 == 4, what will give you newline every 5 lines, starting at 5-th line (count = 4).

"For negative numbers sign of result is implementation defined" This isn't true in C++11 - see ISO14882:2011(e) 5.6-4 or https://stackoverflow.com/questions/7594508. — Tom Swirly, Apr 29 '16 at 22:41
what operands does modulo expects? Why doesn;t it work with float values? — Cătălina Sîrbu, Jan 12 '20 at 18:08

score 7 · Answer 2 · answered Oct 10 '17 at 10:11

Basically modulus Operator gives you remainder simple Example in maths what's left over/remainder of 11 divided by 3? answer is 2

for same thing C++ has modulus operator ('%')

Basic code for explanation

#include <iostream>
using namespace std;


int main()
{
    int num = 11;
    cout << "remainder is " << (num % 3) << endl;

    return 0;
}

Which will display

remainder is 2

score 3 · Answer 3 · answered Sep 23 '12 at 22:52

3

It gives you the remainder of a division.

int c=11, d=5;
cout << (c/d) * d + c % d; // gives you the value of c

answered Sep 23 '12 at 22:52

Gung Foo

13,392
5
31
39

SkySibe · Answer 4 · 2020-06-10T13:36:02.027

3

This JSFiddle project could help you to understand how modulus work: http://jsfiddle.net/elazar170/7hhnagrj

The modulus function works something like this:

     function modulus(x,y){
       var m = Math.floor(x / y);
       var r = m * y;
       return x - r;
     }

edited Jun 10 '20 at 13:36

answered Jul 18 '16 at 07:55

SkySibe

153
1
7

score 2 · Answer 5 · answered Sep 23 '12 at 22:56

You can think of the modulus operator as giving you a remainder. count % 6 divides 6 out of count as many times as it can and gives you a remainder from 0 to 5 (These are all the possible remainders because you already divided out 6 as many times as you can). The elements of the array are all printed in the for loop, but every time the remainder is 5 (every 6th element), it outputs a newline character. This gives you 6 elements per line. For 5 elements per line, use

if (count % 5 == 4)

How does the modulus operator work?

5 Answers5

Linked

Related