Ruby programming problem

Rails
1

I just started to teach myself ruby as a first language from Chris
Pines’s book. There is a exercise to write a program that will
translate arabic numbers to old style roman numbers.
I have completed the exercise and my code is works but only if I type
in numbers that are not divisible by 5. As soon I type in a number
divisible by 5 I get the following error: No implicit conversion from
nil to integer (Type error)
I completely stuck.
I would be really grateful if someone could look at my code and
explain what am I doing wrong.
puts ‘Please type in a number that you would like to be translated’
puts ‘to old style Roman number:’

def romnum leftover
var_i = ‘I’
var_v = ‘V’
var_x = ‘X’
var_l = ‘L’
var_c = ‘C’
var_d = ‘D’
var_m = ‘M’

leftover = ''

leftover = gets.chomp

numb_m  = leftover.to_i / 1000
leftover = leftover.to_i % 1000

if leftover != 0
    numb_d = leftover / 500
    leftover = leftover % 500

    if leftover != 0
        numb_c = leftover / 100
        leftover = leftover % 100

        if leftover != 0
            numb_l = leftover / 50
            leftover = leftover % 50

            if leftover != 0
                numb_x = leftover /10
                leftover = leftover % 10

                if leftover != 0
                    numb_v = leftover / 5
                    leftover = leftover % 5

                    if leftover != 0
                        numb_i = leftover /1
                        leftover = 0
                    end
                end
            end
        end
    end
end


puts var_m * numb_m + var_d * numb_d + var_c * numb_c + var_l *

numb_l + var_x * numb_x + var_v * numb_v + var_i * numb_i
end

romnum 5

2

Ahmy Y.

On Wed, Jan 11, 2012 at 1:43 AM, Loren [email protected] wrote:

       numb_c = leftover / 100
               if leftover != 0
                   numb_v = leftover / 5
                   leftover = leftover % 5

                  # at this line, leftover = 0

end

puts var_m * numb_m + var_d * numb_d + var_c * numb_c + var_l *
numb_l + var_x * numb_x + var_v * numb_v + var_i * numb_i

this line interpret as var_i * nil
hence that error

simple solution is

change it to :

var_i * (numb_i || 0)

that line actually mean :

var_i * numb_i if numb_i is not nil
else var_i * 0

3

On 11 January 2012 11:07, Ahmy Y. [email protected] wrote:

var_i * numb_i if numb_i is not nil
else var_i * 0

Also have a look at the Rails Guide on debugging, that will show you
how to use ruby-debug to break into your code and inspect data, which
will help when you have similar issues again.

Colin

4

Thank you. I will take a look at it.

5

On Wed, Jan 11, 2012 at 06:07, Ahmy Y. [email protected] wrote:

simple solution is

change it to :

var_i * (numb_i || 0)

Even simpler solution is to initialize the variable first. But with
that approach, you should do them all – the current solution will
barf on the first digit past the one that the number is a multiple of.
(That is, if you feed it 30, it will barf due to var_v being nil; if
you feed it 150, it’ll barf due to num_x being nil, etc.)

Another one would be to just output the needed digits immediately,
rather than stashing the number of them and outputting them later.

-Dave

–
Dave A., President, Dave A. Software Engineering and Training
Ruby on Rails Freelancing (Northern Virginia, Washington DC, or Remote)
DaveAronson.com, Codosaur.us, Dare2XL.com, & RecruitingRants.com (NEW!)
Specialization is for insects. (Heinlein) - Have Pun, Will Babble! (me)