From: dblack@...
Date: 2006-11-27T22:47:00+09:00
Subject: Re: simple loops and recursion

Hi --

On Mon, 27 Nov 2006, ishamid wrote:

> Hi,
>
> I'm a total newbie, and this is my very first message. I'm going
> through Chris Pine's Learn to Program; almost half done.
>
> Problem: Consider the following working code:
>
> ===============
> def repeat type
>  number_of_bottles = '99'
>  while number_of_bottles != '0'
>    puts number_of_bottles.to_s + ' bottles:' + ' If one falls, ' +
> (number_of_bottles.to_i - 1).to_s + ' bottles.'
>    type + (number_of_bottles.to_i - 1).to_s + ':'
>    number_of_bottles = gets.chomp
> 	end
> end
>
> repeat 'Type '
> ===============
>
> I want to add a recursion conditional: If there are 98 bottles left,
> one should type '98'; if there are 97, one should type '97' etc. At 0
> bottles the programs ends. What I want is an additional conditional
> recursion, so that e.g. if, at 98 bottles, I type anything other than
> '98', the program recursively tells me to type '98' until I type '98'.
>
> Every way I've tried this gives me a " undefined local variable or
> method `number_of_bottles' " type of error, or else the program keeps
> going back to 99.

Here's a rewrite that might give you some ideas.

   def repeat(prompt)
     bottles = 99
     until bottles.zero?
       expected = bottles-1
       puts "#{bottles} bottles: If one falls, #{expected} bottles."
       print "#{prompt} #{expected}: "
       input = gets.chomp
       until input == expected.to_s
         print "Wrong!  Try again: "
         input = gets.chomp
       end
       bottles = input.to_i
     end
   end

   repeat("Type")


David

-- 
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails"   [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog)        [2] | Co-director, Ruby Central, Inc.   [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org