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newbie adding to array question

Chris Ashton

10/16/2008 2:50:00 PM


hi, i have the following code in my project


def next_seq

x = @current + @previous

@previous = @current

@current = x

end



def display_all

count = 2
while count < @iteration

next_seq

count = count + 1
puts @current

end

end



ive been trying to add the result each time the result is calculated to
array but keep getting stuck

my idea was puttting @fibresults[count] = @current in the while loop,
but i keep getting nil when i try and access it later on

thanks for any help
--
Posted via http://www.ruby-....
9 Answers

Robert Klemme

10/16/2008 3:17:00 PM

0

On 16.10.2008 16:50, Roger Reeks wrote:
> hi, i have the following code in my project
>
>
> def next_seq
>
> x = @current + @previous
>
> @previous = @current
>
> @current = x
>
> end
>
>
>
> def display_all
>
> count = 2
> while count < @iteration
>
> next_seq
>
> count = count + 1
> puts @current
>
> end
>
> end
>
>
>
> ive been trying to add the result each time the result is calculated to
> array but keep getting stuck
>
> my idea was puttting @fibresults[count] = @current in the while loop,
> but i keep getting nil when i try and access it later on

You should disclose more of your code so we can see where it does not
work. There is no @fibresults in the code above so we cannot know what
went wrong.

Cheers

robert

Chris Ashton

10/16/2008 3:36:00 PM

0


@fibresults= []

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


--
Posted via http://www.ruby-....

Robert Klemme

10/16/2008 4:04:00 PM

0

On 16.10.2008 17:36, Roger Reeks wrote:
> @fibresults= []
>
> 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

Here's how you can make your life easier: you do not need @previous and
@current. Instead you only need the array. Note that you can access
elements from the end, i.e. @fibresults[-1] and @fibresults[-2] access
the last and last but one elements.

Another simplification: the while loop can be replaced by

@iteration.times do |count|
end

or

2.upto @iteration - 1 do |count|
end

Kind regards

robert

Mark Thomas

10/16/2008 5:26:00 PM

0

def fib(n)
curr = 0
succ = 1
all = []

n.times do
curr, succ = succ, curr + succ
all << curr
end

all
end

fib(10) #=> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

Brian Candler

10/16/2008 7:53:00 PM

0

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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Brian Candler

10/16/2008 8:06:00 PM

0

Incidentally, I was able to spot the errors very quickly without really
having to think, but ruby will help you if you run it with the -w flag:

ruby -w fib.rb

or

#!/usr/bin/ruby -w
... rest of code

This gives a number of warnings when dubious code runs, in particular it
would have told you where you had mistyped an instance variable name:

fib.rb:10: warning: instance variable @fibresults not initialized

fib.rb:22: warning: instance variable @iteration not initialized

--
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Chris Ashton

10/20/2008 1:17:00 PM

0

thanks for the help up to now, much appreciated

i want to modify the code so it can pu

1.is_fibonacci # returns true
2.is_fibonacci # returns true
3.is_fibonacci # returns false

how could i do that?

thanks again
--
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Brian Candler

10/20/2008 3:19:00 PM

0

Roger Reeks wrote:
> thanks for the help up to now, much appreciated
>
> i want to modify the code so it can pu
>
> 1.is_fibonacci # returns true
> 2.is_fibonacci # returns true
> 3.is_fibonacci # returns false
>
> how could i do that?

class Integer
def is_fibonacci(x=1, y=1)
... put your code here
... the number you are testing is "self"
end
end

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Mark Thomas

10/20/2008 3:21:00 PM

0


> 1.is_fibonacci # returns true
> 2.is_fibonacci # returns true
> 3.is_fibonacci # returns false
>
> how could i do that?

Assuming you mean you want to see if a digit is in the answer (in
which case 3 would actually return true), you can do this:

class Fixnum
def fibonacci?(n=10)
fib(n).include? self
end
end

puts 3.fibonacci?
#=> true
puts 4.fibonacci?
#=> false

-- Mark.