Re: [Pharo-users] mentor question 4

[Roelof Wobben via Pharo-users]

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Op 30-4-2020 om 20:19 schreef Richard Sargent:

See below.

On Thu, Apr 30, 2020 at 10:58 AM Roelof Wobben via Pharo-users <pharo-users@lists.pharo.org> wrote:

and also not with this one :

cardNumber := '4539 1488 0343 6467'.
oddSum := 0.
evenSum := 0.
nextIsOdd := false.
      cardNumber reverseDo: [:digit |
          digit = Character space ifFalse: [
          nextIsOdd
              ifFalse:  [oddSum := oddSum + (digit asString asInteger ) ]
              ifTrue: [(((digit asString asInteger) * 2) > 9)
     ifTrue: [evenSum := evenSum + ((digit asString asInteger)  * 2) - 9 ]
     ifFalse: [ evenSum := evenSum + (digit asString asInteger)  * 2 ]].
             nextIsOdd := nextIsOdd not]].
^ evenSum




Op 30-4-2020 om 18:30 schreef Roelof Wobben:
> Op 30-4-2020 om 16:16 schreef Roelof Wobben:
>> nextIsOdd := true.
>>      aString reverseDo: [:digit |
>>          digit = Character space ifFalse: [
>>          nextIsOdd
>>              ifTrue:  [oddSum := ...]
>>              ifFalse: [evenSum := ...].
>>          nextIsOdd := nextIsOdd not]].
>
> hmm,
>
> Still no luck with this code :
>
> cardNumber := '4539 1488 0343 6467'.
> oddSum := 0.
> evenSum := 0.
> nextIsOdd := true.
>      cardNumber reverseDo: [:digit |
>          digit = Character space ifFalse: [
>          nextIsOdd
>              ifTrue:  [oddSum := oddSum + digit asInteger ]
>              ifFalse: [evenSum := ((digit asInteger * 2) > 9)
>     ifTrue: [evenSum + ((digit asInteger * 2) - 9) ]
>     ifFalse: [ evenSum + (digit asInteger * 2) ]].
>             nextIsOdd := nextIsOdd not]].
> ^ oddSum + evenSum

With the one change to use #digitValue instead of #asInteger (which answers the code point), the above example  works.

| evenSum oddSum |
cardNumber := '4539 1488 0343 6467'.
oddSum := evenSum := 0.
nextIsOdd := true.
cardNumber reverseDo: [:digit |

digit = Character space ifFalse: [

nextIsOdd

ifTrue:  [oddSum := oddSum + digit digitValue ]
ifFalse: [evenSum := ((digit digitValue * 2) > 9)

ifTrue: [evenSum + ((digit digitValue * 2) - 9) ]
ifFalse: [ evenSum + (digit digitValue * 2) ]].

nextIsOdd := nextIsOdd not]].

^ oddSum + evenSum

gives me 80 for the answer.

A few (mostly) minor points:

- I don't see why "reverse" is necessary. Of course if you use #do:, nextIsOdd needs to start with true.

- repeating the "digit digitValue" or other variations adds clutter and reduces clarity

-  ((digit digitValue * 2) - 9) is not unreasonable, but could be simplified. What is the largest integer X such that 2xX<=9?

Reverse is necessary because  the  * 2  needs  to be all even index from the right.

oke, can I then make a temp variable digit which holds the value and rename digit to character because it holding a character instead of a digit

when x is 5 or larger then  2 times the value will be greater then 10.

so the code will be then :

| evenSum oddSum |
cardNumber := '4539 1488 0343 6467'.
oddSum := evenSum := 0.
nextIsOdd := true.
cardNumber reverseDo: [:digit |

  character = Character space ifFalse: [

nextIsOdd
      digit := digit digitValue.

ifTrue:  [oddSum := oddSum + digit ]
ifFalse: [evenSum := (digit >= 5 )

ifTrue: [evenSum + ((digit * 2) - 9) ]
ifFalse: [ evenSum + (digit * 2) ]].

nextIsOdd := nextIsOdd not]].

^ oddSum + evenSum isDivisibleBy: 10.

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