If memory serves me right, module is undefined on negative integers.
int i = -2;
i%=10; // i=undefined?
What should I use instead to get i definitely equal to 7?

On a sidenote, where can I read about operation order/definitions? Like i++, ++i and i%10 not changing i etc.

qwerty:
> If memory serves me right, module is undefined on negative integers.

I think it's defined in D (but it's defined badly).


> int i = -2;
> i%=10; // i=undefined?
> What should I use instead to get i definitely equal to 7?

D outputs -2, Python outputs 8. It's not easy to find a language that outputs 7 there, maybe Malborge language?


> On a sidenote, where can I read about operation order/definitions? Like i++, ++i and i%10 not changing i etc.

D acts like C, here. Even when C does something badly. So you can surely find info about ++ and % in C.

Bye,
bearophile

qwerty wrote:
> If memory serves me right, module is undefined on negative integers.
> int i = -2;
> i%=10; // i=undefined?

It's not undefined.  x%y always has the sign of x, so i will be -2.

This always holds:
x == y * (x/y) + (x%y);
And since D uses truncated division, the result follows.
This behaviour is inherited from C99.

> What should I use instead to get i definitely equal to 7? 

You mean 8?

i %= 10;
if (i<0) i += 10;

> 
> On a sidenote, where can I read about operation order/definitions?
> Like i++, ++i and i%10 not changing i etc. 

bearophile Wrote:

> qwerty:
> > If memory serves me right, module is undefined on negative integers.
> 
> I think it's defined in D (but it's defined badly).
Got url ? :)
> 
> 
> > int i = -2;
> > i%=10; // i=undefined?
> > What should I use instead to get i definitely equal to 7?
> 
> D outputs -2, Python outputs 8. It's not easy to find a language that outputs 7 there, maybe Malborge language?

8 yeah :(somehow I did overcompensated for the max being 9 for %10)

 i      = -3 -2 -1  0  1  2
 i%3 =  7  8  9  0  1  2

So I should be safe with
i % M;
if(i<0) i = M + i;

> 
> > On a sidenote, where can I read about operation order/definitions? Like i++, ++i and i%10 not changing i etc.
> 
> D acts like C, here. Even when C does something badly. So you can surely find info about ++ and % in C.
I'd wish it was available here, as I don't really know C(++).

Don Wrote:

> qwerty wrote:
> > If memory serves me right, module is undefined on negative integers.
> > int i = -2;
> > i%=10; // i=undefined?
> 
> It's not undefined.  x%y always has the sign of x, so i will be -2.
> 
> This always holds:
> x == y * (x/y) + (x%y);
> And since D uses truncated division, the result follows.
> This behaviour is inherited from C99.
Ok, that seems sensible.
Yay,found the spec (mul expressions ?:):
"For integral operands of the / and % operators, the quotient rounds towards zero and the remainder has the same sign as the dividend. If the divisor is zero, an Exception is thrown. "
Personally I find your explanation a lot more clear :)

> 
> > What should I use instead to get i definitely equal to 7?
> 
> You mean 8?
Yeah :(

> 
> i %= 10;
> if (i<0) i += 10;
> 
> > 
> > On a sidenote, where can I read about operation order/definitions? Like i++, ++i and i%10 not changing i etc.
> 

qwerty Wrote:

> bearophile Wrote:
> 
> > qwerty:
> > > If memory serves me right, module is undefined on negative integers.
> > 
> > I think it's defined in D (but it's defined badly).
> Got url ? :)
Yeah, here http://www.digitalmars.com/d/1.0/expression.html#MulExpression