Ruby programming problem

rubyonrails-talk
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 Yulrizka

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

at this line, leftover = 0

if leftover != 0 numb_i = leftover /1 # this line will neger get call, so numb_i is nil 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

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

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

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