From: Jonathan Nielsen <jonathan@...>
Date: 2010-05-19T02:16:09+09:00
Subject: Re: Deaf grandma - almost there

On Tue, May 18, 2010 at 11:04 AM, Stephen Hau <hellostephenhau@gmail.com> wrote:
> From the Chris Pine tutorial for beginners:
>
> **
> Write a Deaf Grandma program. Whatever you say to grandma (whatever
> you type in), she should respond with HUH?!  SPEAK UP, SONNY!, unless
> you shout it (type in all capitals). If you shout, she can hear you
> (or at least she thinks so) and yells back, NO, NOT SINCE 1938! To
> make your program really believable, have grandma shout a different
> year each time; maybe any year at random between 1930 and 1950. (This
> part is optional, and would be much easier if you read the section on
> Ruby's random number generator at the end of the methods  chapter.)
> You can't stop talking to grandma until you shout BYE.
> Hint: Don't forget about chomp! 'BYE'with an Enter is not the same as
> 'BYE' without one!
> Hint 2: Try to think about what parts of your program should happen
> over and over again. All of those should be in your while loop.
>
> **
> Extend your Deaf Grandma program: What if grandma doesn't want you
> to leave? When you shout BYE, she could pretend not to hear you.
> Change your previous program so that you have to shout BYE three times
> in a row. Make sure to test your program: if you shout BYE three
> times, but not in a row, you should still be talking to grandma.
>
> My code is below, and my question is:
> Why can't I reset the 'byes' count to zero using the 'reset' method I've
> defined?
> I know it works when I change the 'else reset' to 'else byes = 0'
>
> byes = 0
>
> def didnthear
>  puts 'SPEAK UP!'
> end
>
> def heard
>    year = (rand(21) + 1930).to_s
>    puts "I heard ya! Not since " + year
> end
>
> def reset
>  byes = 0
> end
>
> while ( byes < 3 )
>  said = gets.chomp
>
>  if said == 'BYE'
>    byes += 1
>  else
>    reset
>  end
>
>  if byes >= 3
>    break
>  end
>
>  if said != said.upcase
>    didnthear
>  else
>    heard
>  end
> end
>
> puts "heard you 3 times, byeeee"

It doesn't work because of scope.  When you set 'byes = 0' in def
reset, you are setting a local variable with scope inside the reset
method.  This is not the same as a local variable in the 'main' scope.

One way to fix this by using an 'instance' scope.  Even though you
aren't technically in a class instance, at some level of abstraction
the default binding is an instance of a class.  So, instead of 'byes'
as a variable, you could use '@byes'.

-Jonathan Nielsen