From: Brian Candler <b.candler@...>
Date: 2008-10-17T04:53:04+09:00
Subject: Re: newbie adding to array question

Roger Reeks wrote:
> 
> @fibresults= []
> 
> def initialize

You don't want to define an initialize method at the top level - only 
inside a class. If I run your code as posted, I get:
fib.rb:3: warning: redefining Object#initialize may cause infinite loop

So the first thing I do is to wrap all this in a class definition (and 
tidy the formatting):

@fibresults= []

class Fib
  def initialize
    @iterations = 10
    @previous = 1
    @current = 1
    @fibresults[0] =@previous
    @fibresults[1] =@current
  end

  def next_seq
    x = @current + @previous
    @previous = @current
    @current = x
  end

  def display_all
    count = 2
    while count < @iteration
    next_seq
    count = count + 1
    @fibresults[count] = @current
    puts @current
   end
  end
end  # class Fib

f = Fib.new
f.display_all

Now it becomes clearer where the problem is:

fib.rb:8:in `initialize': undefined method `[]=' for nil:NilClass 
(NoMethodError)
  from fib.rb:29:in `new'
  from fib.rb:29

You need to move the initialisation of @fibresults *inside* the 
initialize method of the Fib class.

Next bug:

fib.rb:20:in `<': comparison of Fixnum with nil failed (ArgumentError)
  from fib.rb:20:in `display_all'
  from fib.rb:30

That's because you wrote "@iteration" in one place and "@iterations" in 
another.  So I'll change the former to the latter.

At this point the code runs just fine, printing:

2
3
5
8
13
21
34
55

You don't actually make use of the values you stored in the array 
though, so I'll add an accessor to show that they are correct. The code 
now looks like this:

class Fib
  attr_reader :fibresults

  def initialize
    @iterations = 10
    @previous = 1
    @current = 1
    @fibresults= []
    @fibresults[0] =@previous
    @fibresults[1] =@current
  end

  def next_seq
    x = @current + @previous
    @previous = @current
    @current = x
  end

  def display_all
    count = 2
    while count < @iterations
    next_seq
    count = count + 1
    @fibresults[count] = @current
    puts @current
   end
  end
end  # class Fib

f = Fib.new
f.display_all
p f.fibresults

and the results:

2
3
5
8
13
21
34
55
[1, 1, nil, 2, 3, 5, 8, 13, 21, 34, 55]

Oops, an off-by-one error there. You should have assigned to 
@fibresults[count] *before* incrementing count. You can just swap those 
two lines around.

So now your code works. Of course, as others have shown, there are much 
shorter ways of writing this in Ruby. However I think it's of good 
educational value in the first place to get your own code working, 
starting from the way you initially wrote it.
-- 
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