If you have the C99 standard handy anyway, this is clearly stated on page 82
:)

6.5.5.5:
---
The result of the / operator is the quotient from the division of the first
operand by the second; the result of the % operator is the remainder.  In
both operations, if the value of the second operand is zero, the behavior is
undefined.
---

So negatives are allowed in the C99 standard.

I don't have a copy of the C89 standard so I can't quote that one.  Plan 9 C
isn't C99 so I'm not sure any of this is even relevant ot the list.

In The C Programming Language ["draft ANSI Version" that I got from a
college professor who was retiring] it says that  the expression

x % y

produces the remainder when x is divided by y.


Dave

On 12/17/05, David Leimbach <leimy2k@gmail.com> wrote:
>
> C's 'mod' isn't really mod.  It's actually remainder.  It's always been
> this way to my knowledge.
>
> If you want a real "mod" use Python or Ada :)
>
> Dave
>
> On 12/15/05, Jack Johnson <knapjack@gmail.com> wrote:
> >
> > Not really, but all the talk about Singularity got me poking around
> > and I came across this:
> >
> > ------
> >
> > How are the functions DIV and MOD defined?
> >
> > The following answers are given by the Internal Working Document on
> > the Common Language Infrastructure (CLI).
> >
> > result = value1 DIV value2 satisfies the following conditions:
> > |result| = |value1| / |value2|, and
> > sign(result) = +, if sign(value1) = sign(value2)
> > sign(result) = - , if sign(value1) # sign(value2)
> >
> > result  = value1 MOD value2 satisfies the following conditions:
> > result = value1 - value2 * (value1 DIV value2), and
> > 0 <= |result| < |value2|, and
> > sign(result) = sign(value1)
> >
> > Please note that this definition of DIV and MOD differs from the
> > definition given in [M. Reiser, N. Wirth. Programming in Oberon. p.
> > 36]:
> > x  = (x DIV y) * y + (x MOD y), and
> > 0 <= (x MOD y) < y
> >
> > ( from http://www.bluebottle.ethz.ch/oberon.net/faq.html#ad_DivMod )
> >
> > ------
> >
> > I kind of collect random, older computer science texts, so I cracked
> > open The Nature of Computation by Pohl and Shaw, which yields:
> >
> >   "x MOD y = x - (x ÷ y) * y, where ÷ indicates integer division (i.e.
> > fractions are disregarded; equivalently, the result of the division is
> > truncated)."
> >
> > So, what *is* -5 MOD 3?
> >
> > -Jack
> >
>
>