```2010/7/14 Shawn W_ <shawnw / internode.on.net>:
> I have a 2D Array. I have written a method
> the direction given. How do I deal with the boundary conditions without
> receiving an error message.
>
> For example, if I refer to a cell on the top row, and look north there
> will be nothing there, and my program falls over.
>
> I will be creating methods that run over the whole 2D array, replacing
> things in random directions, so when it randomly hits a boundary I need
> my program to ignore cells outside the boundary.
>
> How can I do this? Thx

Did anybody suggest modulo operator so far?  I only glanced over
replies so I might actually have overseen something.  Anyway, you can
see it working here:

irb(main):001:0> a = Array.new(10){|row| Array.new(10) {|col|
"#{row},#{col}"}};nil
=> nil
irb(main):002:0> a.size
=> 10
irb(main):003:0> a[0].size
=> 10

irb(main):012:0> 15.times {|i| printf "%2d %p %p\n",i,a[0][i % 10],a[i % 10][0]}
0 "0,0" "0,0"
1 "0,1" "1,0"
2 "0,2" "2,0"
3 "0,3" "3,0"
4 "0,4" "4,0"
5 "0,5" "5,0"
6 "0,6" "6,0"
7 "0,7" "7,0"
8 "0,8" "8,0"
9 "0,9" "9,0"
10 "0,0" "0,0"
11 "0,1" "1,0"
12 "0,2" "2,0"
13 "0,3" "3,0"
14 "0,4" "4,0"
=> 15

Kind regards

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

```