From: Dave Burt <dave@...>
Date: 2006-03-30T19:18:42+09:00
Subject: Re: Learn to Program, by Chris Pine

Hi Jan,

Have you been typing his examples into IRB and running them as you go? I 
found that technique really useful learning Perl - try variations on the 
example code until you understand it. Try reading Chapter 6 again with IRB, 
including the mini exercise in the Looping section.

But let's unpack your code while it's here:

Jan K wrote:
> Here's what I had when I gave up:
>
> ------------------------------------------
> input = gets.chomp
> number = rand(21)
>
> number2 = 0
> keep_count = 0
>
> if keep_count != 3
> while
> input != 'BYE'
> puts 'HUH?! SPEAK UP, SONNY!'
> keep_count = 0
> input = gets.chomp
> while
>     input == 'BYE'
> puts 'HUH?! SPEAK UP, SONNY!'
> number2 = (keep_count + 1)
> keep_count = number2
> input = gets.chomp
> end
> end
> else
> puts 'NO, NOT SINCE ' + (1930 + number).to_s + '!'
> end
> -----------------------------------------
>
>
> And here's the regular Deaf Grandma solution that I used:
>
> ----------------------------------------
> input = gets.chomp
> number = rand(21)
>
> if
> while
> input != 'BYE'
> puts 'HUH?! SPEAK UP, SONNY!'
> input = gets.chomp
> end
> else
> puts 'NO, NOT SINCE ' + (1930 + number).to_s + '!'
> end
> -------------------------------------

When you start dealing with flow control, you'll find that indenting makes a 
big difference to how easy it is to read and understand your code. Let's 
start by indenting your Grandma code:

if
  while
    input != 'BYE'
    puts 'HUH?! SPEAK UP, SONNY!'
    input = gets.chomp
  end
else
  puts 'NO, NOT SINCE ' + (1930 + number).to_s + '!'
end

Note in all Chris' examples, "if" and "while" are always followed by a 
condition. If Ruby expects something, but doesn't get it, it'll wait until 
the following line. That's what's happening with your if and while. It's the 
same as this:

if (while input != 'BYE'
      puts 'HUH?! SPEAK UP, SONNY!'
      input = gets.chomp
    end)
else
....

See, while's condition is "input != 'BYE'", and if's condition is the result 
of the whole while loop. The result of a while loop is always nil, so the 
condition is always false, so you get 'NO, NOT SINCE'...

That means this section of your program is the same as this:

while input != 'BYE'
  puts 'HUH?! SPEAK UP, SONNY!'
  input = gets.chomp
end
puts 'NO, NOT SINCE ' + (1930 + number).to_s + '!'

Indenting and putting the condition on the same line as the "if" or "while" 
make the flow of your other program a little easier to see, too.

if keep_count != 3
  while input != 'BYE'
    puts 'HUH?! SPEAK UP, SONNY!'
    keep_count = 0
    input = gets.chomp
    while input == 'BYE'
      puts 'HUH?! SPEAK UP, SONNY!'
      number2 = (keep_count + 1)
      keep_count = number2
      input = gets.chomp
    end
  end
else
  puts 'NO, NOT SINCE ' + (1930 + number).to_s + '!'
end

Note you've got a loop inside a loop. To get out of that, the inside loop 
has to exit, and then the outside loop, and if you look at their respective 
conditions (input == 'BYE') and (input != 'BYE'), that will never happen.

Try going back to the example in the Looping section, and modifying that 
little bits at a time. Indent lines inside control structures to help you 
see at a glance where they begin and end.

Cheers,
Dave