From: Josh Cheek <josh.cheek@...>
Date: 2009-08-25T03:42:03+09:00
Subject: Re: Array Troubles

--000e0cd6cef8c4eaac0471e792da
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

On Mon, Aug 24, 2009 at 3:57 AM, Scott Andrechek
<scottandrechek@gmail.com>wrote:

> I've made this small table making program (not reall trademarked) and
> have been trying to add the ability to make your own title. Every time
> it goes to make the table i get this message: tablemaker.rb:38:
> undefined method `rjust' for nil:NilClass (NoMethodError). Here is the
> code:
>
> thisisthewordpage=['page']
> thisisthetitle=[]
> tableZZZ=0
> tableZZ=0
> tableZ=0
> pagesZ=0
> pagesZZ=0
> play=true
> puts 'Please type your title for your table (if you type nothing the
> title will be Table of Contents)'
> toptitle=gets.chomp
> if toptitle==''
> toptitle='Table of Contents'
> thisisthetitle.push toptitle
> if toptitle !=''
> thisisthetitle.push toptitle
> end
> end
> puts 'Please type your titles in first'
> table= []
> while (title=gets.chomp)!= ''
> table.push title
> tableZ+=1
> end
> puts 'Please type your page numbers'
> pages= []
> puts table[tableZZZ]
> while (page=gets.chomp)!= ''
> tableZZZ+=1
> puts table[tableZZZ]
> pages.push page
> pagesZ+=1
> end
> linewidth0=55
> linewidth1=45
> linewidth2=60
> linewidth3=10
> linewidth4=5
> puts (thisisthetitle[0].rjust(linewidth1)) # This is line 38
> while play==true
>  if tableZ!=0
>  puts (table[tableZZ].ljust(linewidth2))+
> (thisisthewordpage[0].rjust(linewidth3)) + '' +
> (pages[pagesZZ].rjust(linewidth4))
>  tableZ+=-1
>  tableZZ+=1
>  pagesZ+=-1
>  pagesZZ+=1
>  if tableZ==0
>    play=false
>  end
> end
> end
> if play==false
> puts ''
> puts 'Table Created by Table MakerTM'
> end
>
> Any help as always is greatly appreciated.
> -Scott Andrechek
> --
> Posted via http://www.ruby-forum.com/.
>
>
Hi, Scott,
The ruby syntax is
if
elsif
else
end

In your example, you did
if toptitle==''
   if toptitle !=''
  end
end

So you were actually nesting if statements. However the inner if statement
was guaranteed to never be true, because it was the negation of the first if
statement. What you could do instead is
if toptitle == ''
else  #by default, this means that toptitle!=''
end

I refactored the code a bit (I tried not to vary too much from your format).
There were some places that were getting a little bit convoluted, keeping
track of lots of counters, and incrementing / decrementing them as you went
through the array. There were also some variables that I thought would be
better off being a different type. I renamed some variables to follow more
rubyish conventions.



# get the table title
puts 'Please type the title for your table (if you type nothing the title
will be Table of Contents)'
table_title = gets.chomp  # not really any need to put this variable into an
array

table_title = 'Table of Contents' if table_title.empty? #empty string will
return true

# get the chapter titles, place them into the array
# split turns our string into an array, it uses a comma for a delimiter
because I passed it
#   a comma in a string.
# map! just loops through each element in the array, and replaces the array
element with
#   the last line of the submitted block.
#   the ! indicates that it does it to the array we are calling it on.
Without the !, it would
#   return a new array with those elements
#   the |t| says that we want to access the current element (a title)
through a variable named t
# strip removes leading and tailing whitespace from a string
# documentation for split
http://www.ruby-doc.org/core/classes/String.html#M000803
# documentation for map!
http://www.ruby-doc.org/core/classes/Array.html#M002190
# documentation for strip
http://www.ruby-doc.org/core/classes/String.html#M000820
puts 'Please type your titles in one line, separated by commas.'
table = gets.split(',').map!{|t| t.strip}  # so this could be expressed in
English as "get the next line,
                                           # split it into an array of
titles, and replace each title in
                                           # the array with the same title,
after whitespace has been removed"
                                           # this is also why we don't have
to say gets.chomp, because \n is whitespace


# get the page numbers
# replace the chapter titles with an array containing the chapter title, and
the page number
# note that map!{...} and map do ... end can both be used,
# I usually use {} for single line blocks, and do end for multi line blocks
puts 'Please type your page numbers'
table.map! do |chapter_title|
  print "The page number for " + chapter_title.inspect + " should be: "
  [chapter_title , gets.chomp]
end



# initializations for printing out the table

# I think a hash makes a lot of sense here, because you were having to
remember that specific numbers
# correllate to specific places to use the line widths, if we use a hash, we
can essentially label which
# values are which. For our keys, we use symbols, these are similar to
strings, but they all point to
# the same object. (you could replace them with strings if it made you feel
more comfortable)
# documentation for hash http://www.ruby-doc.org/core/classes/Hash.html
# documentation for Symbol http://www.ruby-doc.org/core/classes/Symbol.html
line_widths = { :table_title    =>  45 ,
                :chapter_title  =>  60 ,
                :word_page      =>  10 ,
                :page_number    =>  5  }

word_page = 'page' # not really any need for this variable to be an array


# print out the table title
puts
puts table_title.rjust( line_widths[:table_title] ) #pull the appropriate
width from the hash, notice how
                                                    #much it looks like
accessing an index in an array

# print out the table
# here we use the each method, which loops through each element in the array
# we pass it a block by using do |parameters| ... end
# in this case, we are receiving one parameter, the array [chapter_title ,
page_number]
# this was set back when we took the page numbers
# we can group our parameters together with () so that this ultimately
becomes
# chapter_title , page_number = [ "some chapter title" , "12" ]
# which is a common Ruby way of assigning values, try it out if you like.
table.each do |(chapter_title,page_number)|
  #when the argument is the last thing on the line, you don't actually need
parentheses
  print chapter_title.ljust line_widths[ :chapter_title ]
  print word_page.rjust     line_widths[ :word_page     ]
  puts  page_number.rjust   line_widths[ :page_number   ]
end
puts
puts 'Table Created by Table MakerTM'

# now, for some real fun, you should try turning it into a class ^_^

--000e0cd6cef8c4eaac0471e792da--