From: mark sparshatt <msparshatt@...>
Date: 2004-09-17T05:32:32+09:00
Subject: Re: 2-d arrays

Barry Sperling wrote:

>
>     Reading the recent posts about ant-wars, I thought that, as a 
> nuby, it would be interesting to try to recreate the ant-wars engine.  
> I looked at their code a little, and then started in.  I appreciate 
> that James Edward Gray II provided us with his code, but I'll look at 
> it after I've made more progress.
>     I decided to create 2-d arrays to hold the data for given 
> positions ( hexagonal blocks ).  One would hold the amount of food at 
> a position, another would hold the traversability of it, etc.  My 
> first attempt failed in a strange way and the point of this email is: 
> why?
>
> Method 1
>
> cols = 10
> empty_row_int = Array.new( cols, 0 )

this creates an array

> $food_layout = Array.new
> rows.times { $food_layout.push( empty_row_int ) }

this pushes that array into $food_layout rows times.

> puts $food_layout[ 0 ][ 0 ]  # 0
> $food_layout[ 0 ][ 0 ] = 6   # SET FOOD ITEMS IN HEXAGON
> puts $food_layout[ 0 ][ 0 ]  # 6
> puts $food_layout[ 1 ][ 0 ]  # 6   WRONG!
>
$food_layout[0] and $food_layout[1] both refer to the same array object 
(empty_row_int) so they both hold the same values.

The correct way to do this would be

cols = 10
$food_layout = Array.new
rows.times { $food_layout.push( Array.new( cols, 0 ) ) }
puts $food_layout[ 0 ][ 0 ]  # 0
$food_layout[ 0 ][ 0 ] = 6   # SET FOOD ITEMS IN HEXAGON

HTH

--
Mark Sparshatt