Re: Need Help On Ada95 Problem

[Shark8 <onewingedshark@gmail.com>]

On Feb 8, 7:03 pm, Will <willmann...@gmail.com> wrote:
> I am new to Ada and need help on an exercise for school.  Can anyone
> help.  The problem is as follows ( you can skip all the build up
> background A Christmas Story references):
>
> Problem 1: Secret Decoder Ring
>
> You may remember Ralphie's disappointment when he received his Little
> Orphan Annie Secret Decoder Ring.
> What you may not realize is that, after Ralphie threw away his ring,
> his brother Randy dug it out of the trash. Randy grew up to run the IT
> department of his small hometown bank, and was responsible for storing
> the 4-digit Personal Identification Numbers (PINs) chosen by his
> bank's customers. He knew better than to store these PINs in the
> clear, so he encrypted them using Ralphie's ring.
>
> The decoder ring had two wheels, one printed with letters and one
> printed with numbers. In the video clip, you see Ralphie decoding the
> numbers read on the radio, looking up each number and copying down the
> corresponding letter. Randy uses the ring in a similar way, but
> instead of disguising letters as numbers, he does the reverse,
> disguising numbers as letters. To encrypt a PIN, he finds each digit
> on the wheel, and turns it into a letter. (The ring contains some two-
> digit numbers as well, but he ignores those, using only the single-
> digit numbers.)
>
> Here is a small portion of the decoder ring:
>
>      number wheel ->    0  1  2  3  4  5  6  7  8  9
>      letter wheel ->    U  R  O  V  A  L  T  I  N  E
>
> So, for example, Randy encrypts the PIN 9537 as ELVI.
>
> Complete the function Encrypt(PIN) that takes a 4-digit PIN (as a
> string) and returns the corresponding 4-letter code (also as a
> string).
>
> Note: It would be possible to convert digits to letters using a giant
> IF statement, but don't do this. Instead, the letter wheel is given to
> you as a string, so use each digit to read the appropriate letter from
> the string.

Alright this is actually a simple problem; there are several ways to
go about this,
but let's play to Ada's strengths and use types.

So start by describing things in terms of types.

      Type Cypher_Character is Private;
      Type Pin_Character is Private;

      Type Pin_String is Array(1..4) of Pin_Character;

--- Later in the private section.
      Type Cypher_Character is new Character;
      Type Pin_Character is new Character;

In this mindset things become crystal clear: this is merely type-
conversion.

So you'll need a conversion function, something like:

  Function Convert_Pin_Character( Item : In Pin_Character ) Return
Cypher_Character;

with an implementation of:
  Function Convert_Pin_Character( Item : In Pin_Character ) Return
Cypher_Character is
  begin
   Return Result : Cypher_Character do
      ----- ACTUAL CONVERSION GOES HERE
   end return;
  end;

Reading the problem the note says:
It would be possible to convert digits to letters using a giant
IF statement, but don't do this. Instead, the letter wheel is given to
you as a string, so use each digit to read the appropriate letter from
the string.

Meaning that they're hinting strongly that you use the CASE statement.