From: Bertram Scharpf <lists@...>
Date: 2009-12-30T02:55:30+09:00
Subject: Re: Question abour rand()

Hi,

Am Dienstag, 29. Dez 2009, 18:51:53 +0900 schrieb Panagiotis Atmatzidis:
> I'm looking for a way to create a random sequence of numbers using the 'rand' method. I can think of something like:
> 
> -----
> while pipi == TRUE
>   if x > 1950 || x < 2000
>      return  x
>      pipi = FALSE
> ------
> 
> Since however the book that I'm reading has not introduced while/else/if etc. I'm thinking that there must be an easier and probably more sensible way to approach this. As far as I've read rand(2000) will give random numbers from 0-to-2000 no matter what.
> 
> NOTE:  I don't want to use another method just to do the job.
> 
> thanks in advance & best regards

The "rand" method has been mentioned. Here are just some
considerations about the above code.

You don't need a loop for calculating a random value. (There is a
random algorithm below.) But when use a loop, then you either say
"return" or leave it by a condition but not both.

  cond = true
  while cond do
    ...
    if some_condition then
      cond = false
    end
    ...
  end

_or_

  loop do
    ...
    break if some_condition
    ...
  end

Note that "break" can even return values:

  result = loop do
    break "hi"
  end
  result == "hi"

And here is an example of a very simple random implementation:

  class R
    def initialize
      @r = 0
    end
    def nextval
      @r =  ((@r * 0xabcd) + 0x73737) % 0x1_0000_0000
      @r >> 16 
    end
  end
  r = R.new
  new_random_value = r.iterate
  random_value_below_fifty = r.iterate % 50

Bertram


-- 
Bertram Scharpf
Stuttgart, Deutschland/Germany
*
Discover String#notempty? at <http://raa.ruby-lang.org/project/step>.