# Forum: Ruby Modulo ?

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on 2009-03-19 07:51
```Maybe i need to get some sleep, but can someone explain how modulos
work?

Thanks```
on 2009-03-19 08:18
```Zayd C. wrote:
> Maybe i need to get some sleep, but can someone explain how modulos
> work?
>
> Thanks

result = 7 % 3
puts result

--output:--
1

7 has two 3's in it, and after removing those two 3's from 7, the
remainder is 1.```
on 2009-03-19 15:50
```Zayd C. <removed_email_address@domain.invalid> writes:

> Maybe i need to get some sleep, but can someone explain how modulos
> work?

From "Discrete Mathematics by Rosen":

"Let a be an integer and m be a positive integer. We denote by a mod m
the remainder when a is divided by m.

It follows from the definition of remainder that a mod m is the
integer r such that:

a = q * m + r and 0 <= r < m "

This is all assuming you didn't type an 'o' when you meant 'e' ;)```
on 2009-03-19 16:26
```On 19.03.2009 06:50, Zayd C. wrote:
> Maybe i need to get some sleep, but can someone explain how modulos
> work?

http://lmgtfy.com/?q=modulo```
on 2009-03-19 16:43
```On Mar 19, 2009, at 10:22 AM, Robert K. wrote:

> On 19.03.2009 06:50, Zayd C. wrote:
>> Maybe i need to get some sleep, but can someone explain how modulos
>> work?
>
> http://lmgtfy.com/?q=modulo
>

This seems completely unnecessary.  There was already a great response
from Brian who not only directly addressed the "modulos", but also
picked up and pointed out (subtly) that the question might have been
about "modules". Something that makes perfect sense, but I certainly
didn't see that possibility.

And did you Google modulo or module yourself to see how useful the
result really is? If you're going to simply shout lmgtfy, at least put
"ruby" in there, too (well, for module, not for modulo ;-)

-Rob

Rob B.    http://agileconsultingllc.com
on 2009-03-19 17:05
```On 19.03.2009 15:40, Rob B. wrote:
> And did you Google modulo or module yourself to see how useful the
> result really is?

I did.

robert```
on 2009-03-19 17:15
```Rob B. wrote:
> On Mar 19, 2009, at 10:22 AM, Robert K. wrote:
>
>> On 19.03.2009 06:50, Zayd C. wrote:
>>> Maybe i need to get some sleep, but can someone explain how modulos
>>> work?
>>
>> http://lmgtfy.com/?q=modulo
>>
>
>
> This seems completely unnecessary.  There was already a great response
> from Brian who not only directly addressed the "modulos", but also
> picked up and pointed out (subtly) that the question might have been
> about "modules". Something that makes perfect sense, but I certainly
> didn't see that possibility.
>
> And did you Google modulo or module yourself to see how useful the
> result really is? If you're going to simply shout lmgtfy, at least put
> "ruby" in there, too (well, for module, not for modulo ;-)
>
> -Rob
>
> Rob B.    http://agileconsultingllc.com

Thanks guys,(singing) I can see clearly now the rain is gone :). Maybe I
should have been more clear and added the % sign when mentioning modulo,
so I wouldn't confuse anyone thinking I meant modules :)

Thanks```
on 2009-03-19 22:02
```> Thanks guys,(singing) I can see clearly now the rain is gone :). Maybe I
> should have been more clear and added the % sign when mentioning modulo,
> so I wouldn't confuse anyone thinking I meant modules :)
>
> Thanks
>
>
Though there is one thing I would like to point out: 0 % 7 = 0
So 'remainder' is not strictly true

Michael

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on 2009-03-19 22:53
```Michael M. wrote:
> Though there is one thing I would like to point out: 0 % 7 = 0
> So 'remainder' is not strictly true

Sorry I don't follow you. What's the remainder of 0/7 if not 0?
0-7*0 is 0, is it not?

Confused,
Sebastian```
on 2009-03-19 23:11
```Sebastian H. wrote:
> Sebastian
>
>
Many people I know and work with simplify the modulo operator to
themselves as remainder, so mentally (whether or not it is correct)
assume 0/7 = 0 r 7
I am just making an explicit example of this not necessarily obvious
case.  It's totally fine when one knows the semantics of modulo, it's
the simplification to remainder that many people make that causes
problems here.

Michael

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on 2009-03-19 23:45
```On Mar 19, 2009, at 5:07 PM, Michael M. wrote:

>> Confused,
>
> Michael

[I hope this survives email formatting...]

__0_r_0_
7 ) 0
0*7 =>  -0
==
0

Just because people can't understand division and remainders isn't
enough to keep them away from technical discussions. The original
response (which I deleted months ago [or was that yesterday?]) had an
accurate definition.

-Rob

Rob B.    http://agileconsultingllc.com
on 2009-03-20 00:06
```Michael M. wrote:
> Many people I know and work with simplify the modulo operator to
> themselves as remainder, so mentally (whether or not it is correct)
> assume 0/7 = 0 r 7

Maybe I'm slow, but I don't get it.
You're saying that many people assume that x % y is the same as the
remainder
of dividing x by y, right? I don't see anything wrong with that.
If I understand you correctly, you're also saying that this assumption
is
wrong in the case of 0%7. I don't understand why that should be the
case. The
remainder of 0/7 is 0, right? And 0%7 is also 0, so where's the problem?

Still confused,
Sebastian```
on 2009-03-20 00:18
```Sebastian H. wrote:
> If I understand you correctly, you're also saying that this assumption is
> wrong in the case of 0%7. I don't understand why that should be the case. The
> remainder of 0/7 is 0, right? And 0%7 is also 0, so where's the problem?
>
> Still confused,
> Sebastian
>
>
Sorry for confusing everyone here, I just know of a particular case
where 0%7 = 7 was assumed.  I was trying to stop this happening again,
but I think I've caused more confusion than it's worth.  Sorry folks.
Ignore my post and you'll sleep more easily.

Michael

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lost by reason of this transmission.
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on 2009-03-20 00:25
```Robert K. <removed_email_address@domain.invalid> writes:

> On 19.03.2009 06:50, Zayd C. wrote:
>> Maybe i need to get some sleep, but can someone explain how modulos
>> work?
>
> http://lmgtfy.com/?q=modulo

That is *awesome* !  Sponsored by "Backpack" - interesting.```
on 2009-03-20 04:10
```On 3/19/09 6:03 PM, Sebastian H. wrote:
> remainder of 0/7 is 0, right? And 0%7 is also 0, so where's the problem?
Going by the usual definition of "remainder", there is a difference
between modulo and remainder when negative numbers get involved.

remainder(a,b) = a - trunc(a/b) * b
modulo(a,b) = a - floor(a/b) * b```
on 2009-03-20 04:58
```On Mar 19, 5:15 pm, Michael M. <removed_email_address@domain.invalid> wrote:
> Sorry for confusing everyone here, I just know of a particular case
> where 0%7 = 7 was assumed.

This is confusing. As in 0%7 = 7 is very confusing.

A mod B shouldn't have a result that's equal to or greater than B. If
that happens, you take a B out until you can't anymore. The remainder
when A is divided by B is the same thing. If you end up with something
greater than B, you stopped too soon.

As John W. Kennedy pointed out, the difference between modulo and a
simple remainder comes up when dealing with negative numbers.```
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