Pushing things Arrays

ruby-talk
1

I've been learning Ruby and have done a couple of the quizes on the
rubyquiz.com web site and written a couple of my own. Recently, I was
surfing and stumbled on Graham King's credit card generator <
http://www.darkcoding.net/projects/credit-card-generator/> He included
several versions including PHP, Python and Java, but not Ruby. I thought it
would be a good exercise translating it into Ruby and started working on it.
What I thought would be an exercise that would take a couple of hours has
now taken a few days, and I'm stumped.
The problem involves the arrays used to hold the prefixes for the different
cards. For some reason the program changes the original prefix so if a
prefix is called that was called before it uses the entire randomly selected
number.
--snip--
American Express

···

----------------
345258182650083
377822445136536
3778224451365361
3452581826500839
34525818265008392

Discover
--------
6011448520213005
60114485202130056
601144852021300560

Diners Club / Carte Blanche
---------------------------
30232254153565
30032768147008
38878817351526
--snip--

I think the part that is causing problems is in here:

def completed_number(prefix, len)
        newCcnumber = []
    newCcnumber = prefix
        len = len

    # generate digits

    while newCcnumber.length < (len - 1)
            ran = rand(9)
            newCcnumber.push(ran).to_s
        end

    #reverse number
    reversedCCnumber = newCcnumber.reverse

    #calculate sum

    sum = 0
    pos = 0

    while pos < (len - 1)

        odd = (reversedCCnumber[pos].to_i) * 2
        if odd > 9
            odd -= 9
        end

        sum = sum + odd;

        if pos != (len - 2)

            sum = sum + (reversedCCnumber[pos +1]).to_i
        end
        pos += 2
    end
    #calculate check digit

    checkdigit = (((sum/10) + 1) * 10 - sum) % 10

    newCcnumber.push(checkdigit)

        newCcnumber = newCcnumber.to_s+"\n"
end

I don't really want a full solution to this problem, since I started it as a
learning exercise. What I would like is a push in the right direction. What
am overlooking? Am I way off on this problem or is it just something simple
that I'm missing?

amexPrefixList = [ ['3', '4'],
                    ['3', '7'] ]

discoverPrefixList = [ ['6', '0', '1', '1'] ]

dinersPrefixList = [ ['3', '0', '0'],
                        ['3', '0', '1'],
                        ['3', '0', '2'],
                        ['3', '0', '3'],
                        ['3', '6'],
                        ['3', '8'] ]

2

These lines look VERY suspicious:
newCcnumber = []
newCcnumber = prefix

**hint: newCcnumber and prefix are variables which *refer to the same
object* after the last statement

3

Wally Terrible wrote:

I've been learning Ruby and have done a couple of the quizes on the

yes

    newCcnumber =
    newCcnumber = prefix

now newCcnumber and prefix refer the same array

        newCcnumber =
    newCcnumber.concat prefix # append the elements of prefix to
newCcnumber

newCcnumber and prefix refer to different array

tiziano

···

--
Posted via http://www.ruby-forum.com/\.

4

Thanks. That was it. I suspected I was overlooking something simple. Now it's working as expected.