I have a simpleish bit of code here that always seems to give me an error, and i can't figure out quite why. If I have a constant 43 in the modulo if breaks. however if i use points.length it seems to be ok?

import std.stdio;
void main(){
	int points[43] = [0, 1153, 1905, 1996, 1392,  305, -888,-1773,-2041,-1600, -603,  603, 1600,2041, 1773,  888, -305,-1392,-1996,-1905,-1153, -0,1153, 1905, 1996, 1392,305, -888,-1773,-2041,-1600, -603,  603, 1600, 2041, 1773,  888, -305,-1392,-1996,-1905,-1153,    0];
	
	foreach(int x; points){
		writeln("List Value: ",points[(x%43)],"\t");
	}

}

On Wednesday, 11 June 2014 at 22:32:45 UTC, Taylor Hillegeist wrote:
> I have a simpleish bit of code here that always seems to give me an error, and i can't figure out quite why. If I have a constant 43 in the modulo if breaks. however if i use points.length it seems to be ok?
>
> import std.stdio;
> void main(){
> 	int points[43] = [0, 1153, 1905, 1996, 1392,  305, -888,-1773,-2041,-1600, -603,  603, 1600,2041, 1773,  888, -305,-1392,-1996,-1905,-1153, -0,1153, 1905, 1996, 1392,305, -888,-1773,-2041,-1600, -603,  603, 1600, 2041, 1773,  888, -305,-1392,-1996,-1905,-1153,    0];
> 	
> 	foreach(int x; points){
> 		writeln("List Value: ",points[(x%43)],"\t");
> 	}
>
> }

Perhaps i am stupid....
0..points.length lol? i've been looking at this too long.

On Wednesday, 11 June 2014 at 22:35:39 UTC, Taylor Hillegeist wrote:
> On Wednesday, 11 June 2014 at 22:32:45 UTC, Taylor Hillegeist wrote:
>> I have a simpleish bit of code here that always seems to give me an error, and i can't figure out quite why. If I have a constant 43 in the modulo if breaks. however if i use points.length it seems to be ok?
>>
>> import std.stdio;
>> void main(){
>> 	int points[43] = [0, 1153, 1905, 1996, 1392,  305, -888,-1773,-2041,-1600, -603,  603, 1600,2041, 1773,  888, -305,-1392,-1996,-1905,-1153, -0,1153, 1905, 1996, 1392,305, -888,-1773,-2041,-1600, -603,  603, 1600, 2041, 1773,  888, -305,-1392,-1996,-1905,-1153,    0];
>> 	
>> 	foreach(int x; points){
>> 		writeln("List Value: ",points[(x%43)],"\t");
>> 	}
>>
>> }
>
> Perhaps i am stupid....
> 0..points.length lol? i've been looking at this too long.

	foreach(uint x; points){
		writeln("List Value: ",points[(x%43)],"\t");
	}

this must work because its a different type than an element in points[]

On Wednesday, 11 June 2014 at 22:38:02 UTC, Taylor Hillegeist wrote:
> On Wednesday, 11 June 2014 at 22:35:39 UTC, Taylor Hillegeist wrote:
>> On Wednesday, 11 June 2014 at 22:32:45 UTC, Taylor Hillegeist wrote:
>>> I have a simpleish bit of code here that always seems to give me an error, and i can't figure out quite why. If I have a constant 43 in the modulo if breaks. however if i use points.length it seems to be ok?
>>>
>>> import std.stdio;
>>> void main(){
>>> 	int points[43] = [0, 1153, 1905, 1996, 1392,  305, -888,-1773,-2041,-1600, -603,  603, 1600,2041, 1773,  888, -305,-1392,-1996,-1905,-1153, -0,1153, 1905, 1996, 1392,305, -888,-1773,-2041,-1600, -603,  603, 1600, 2041, 1773,  888, -305,-1392,-1996,-1905,-1153,    0];
>>> 	
>>> 	foreach(int x; points){
>>> 		writeln("List Value: ",points[(x%43)],"\t");
>>> 	}
>>>
>>> }
>>
>> Perhaps i am stupid....
>> 0..points.length lol? i've been looking at this too long.
>
> 	foreach(uint x; points){
> 		writeln("List Value: ",points[(x%43)],"\t");
> 	}
>
> this must work because its a different type than an element in points[]

Negative indexes are possible with modulo... that is why i am getting breaking... sorry all.

On Wednesday, 11 June 2014 at 22:32:45 UTC, Taylor Hillegeist wrote:
> I have a simpleish bit of code here that always seems to give me an error, and i can't figure out quite why.
modulo takes the sign of the dividend:
http://en.wikipedia.org/wiki/Modulo_operation#Common_pitfalls

It works with length because you introduce a signed -> unsigned conversion.

modulo of a negative number can give some surprising results. A negative index in that array would cause it to throw a range error, so my guess is that's what you're getting. If you do %array.length though it becomes an unsigned math and thus will never be negative, explaining the different result.

Remember btw that when foreaching over an array, the value you get is the number in the array, not the index.