From: Matthew Smillie <M.B.Smillie@...>
Date: 2006-06-27T03:42:11+09:00
Subject: Re: Stumped:beginners question

On Jun 26, 2006, at 19:26, Dark Ambient wrote:

> On 6/26/06, Rob Biedenharn <Rob@agileconsultingllc.com> wrote:
>> OK, first I just *have* to ask:  Do you have a copy of Programming  
>> Ruby?
>>
>> No?  Get the first edition here: http://www.ruby-doc.org/docs/
>> ProgrammingRuby/
>>
>> keep reading...!
>>


> This is the while explanation (most of it) from PR 2nd edition ,  
> which I own.
>
> while boolean-expression [ do | : ]
> body
> end
> executes body zero or more times as long as boolean-expression is  
> true.
> until boolean-expression [ do | : ]
> body
> end
>
> It doesn't help me one bit (literally), not with correctly setting  
> up the loop.


Your biggest problem in the code you put up is that you're using the  
same variable for several different things: a (apparently redundant)  
parameter to the method, a loop condition, and to hold user input -  
it's much better, especially when you're learning to program, to use  
separate variables for these separate concerns.

There are several problems with the code, one of which is (again) the  
bad choice of loop condition, observe your code stripped down to only  
the bits which affect the loop continuing or not:

sort = ''
while sort == ''
   sort = gets.etc.etc  # sort != ''
end

So, at the end of the loop, sort != '', and the loop terminates.  The  
answer (again) is to pick a loop condition that you know will be true  
as long as you want the loop to continue.  This is pretty accurately  
described in the excerpt you posted - for the first loop, the  
condition is true, so the body executes.  For the next iteration, the  
condition is false, so the loop body doesn't execute, and the program  
continues.

matthew smillie.