From: Joe Van Dyk <joevandyk@...>
Date: 2005-12-22T08:16:23+09:00
Subject: Re: String > Integer Conversion Problem

On 12/21/05, Joe Van Dyk <joevandyk@gmail.com> wrote:
> On 12/21/05, Matthew Feadler <matthew@feadler.com> wrote:
> > Retro thanks to all who helped me with my last post.  I'm certainly more
> > comfortable with Ruby now than then, but still a newbie as the following
> > will surely demonstrate.
> >
> > Below, you can see that I'm checking command-line arguments to the
> > program for various conditions.  Unfortunately, because the args are
> > stored as strings, when I convert them via to_i, empty and non-numerical
> > strings become 0.  0 is an acceptable element in this program, therefore
> > I can't use it to test for invalid input.  I've worked around this (sort
> > of), by creating two sets of variables for the arguments (one set as
> > strings, one set as integers).  Unfortunately, this complicates the
> > code, and more importantly, leaves me stumped concerning how to test for
> > non-numeric values.
> >
> > So, the program does what I want, except when the args are non-numeric
> > strings, and the code seems uglier than it ought to be.
> >
> > Thanks in advance,
> >
> > -ELf
> >
> > def gen_chart(max)
> >   x=0
> >   y=0
> >   local_chart = Array.new
> >   while x<=max
> >     y+=x
> >     local_chart[x]=y
> >     x+=1
> >   end
> >   local_chart
> > end
> >
> > arg0 = ARGV[0]
> > arg1 = ARGV[1]
> >
> > arg0i = ARGV[0].to_i
> > arg1i = ARGV[1].to_i
> >
> > if arg0.nil? or (arg0i < 0) or (arg1i < 0)
> >   #print usage
> >   print <<-EOS
> >
> > No args, or bad args!
> >
> > Usage: #$0 [maxvalue]
> >        #$0 [minvalue] [maxvalue]
> >   EOS
> > elsif arg1.nil?
> >   #do chart to arg0, print last pair
> >   chart = gen_chart(arg0i)
> >   puts arg0i.to_s + ": " + chart[arg0i].to_s
> > else
> >   #do chart to arg1, print pairs from arg0 to last
> >   chart = gen_chart(arg1i)
> >   x=arg0i
> >   y=arg1i
> >   while x<=y
> >     puts x.to_s + ": " + chart[x].to_s
> >     x+=1
> >   end
> > end
>
> Maybe this will give you an idea or two:
>
> require 'test/unit'
>
> def process_command_line_arguments args
>   results = []
>   args.each do |arg|
>     raise "Hey, '#{ arg }' needs to be a number" if !arg.match(/^\d*$/)
>     arg = arg.to_i
>     results << arg
>   end
>   results
> end
>
> class TestThis < Test::Unit::TestCase
>   def test_command_line_processing
>     assert_equal [2],    process_command_line_arguments(["2"])
>     assert_equal [2, 3], process_command_line_arguments(["2", "3"])
>     assert_raise(RuntimeError) { process_command_line_arguments(["-1"]) }
>     assert_raise(RuntimeError) { process_command_line_arguments(["1", "oog"]) }
>     assert_raise(RuntimeError) { process_command_line_arguments(["boo", "oog"])}
>   end
> end
>
>
>
> $ ruby a.rb
> Loaded suite a
> Started
> .
> Finished in 0.001163 seconds.
>
> 1 tests, 5 assertions, 0 failures, 0 errors
>

Whoops, this is probably better:

def process_command_line_arguments args
  args.map do |arg|
    raise "Hey, '#{ arg }' needs to be a number" if !arg.match(/^\d*$/)
    arg.to_i
  end
end

Passes all the tests.