in reply to Re: Perl hex substraction
in thread Perl hex substraction

The problem is I don't know how to do it :)
I have a file with all those hex numbers like I said: 4d 2c 07 2c 77 b3 77 b3 74 81 9d 59 9d 5f 5a 9e 50 94 4e 8a 4e 8a 4e 8c 43 3c 28 1f 1d 5a 3b fe 3a f1 59 c0 9d f3 54 e2 b2 82 da 68 c1 9b ef bf 9d 59 92 a0 2a 6d 29 ed 29 ed 29 ed 29 ed 29 ed 20 e4 13"
The "decrypted" result of the file is every hex number is the result of substracting from itself the next hex number.

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Re^3: Perl hex substraction
by Corion (Patriarch) on Feb 15, 2011 at 12:41 UTC

    How would you do it without a computer? What part of the task do you have difficulties with?

[reply]
      Ok, without computer.
      I have a sentence with numbers like (let's forget about hex):
      50 40 30 12 8 4 2
      I know this is some for of an encrypted message, and to get the message decoded every number must be substracted the next one from it: 
      50 - 40 = 10 
40 - 30 = 10
30 - 12 = 18
12 - 8 = 4
8 - 4 = 4
4 - 2 = 2
2 - 0 = 2

      [download]
      So my result, my decoded sentence would be:
      10 10 18 4 4 2 2
[reply]
[d/l]

        Where do you have problems with implementing this (a bit modified) problem?

        Can you see a way to turn this modified problem into your original problem?

        A first step in solving the problem could be to get at the numbers from the string.

[reply]
      Let's say I have these hex numbers in a list or array:
      4d 2c 07 2c 77
      Every number in this array should be substracted from it the next one to it like:
      4d - 2c = 21
      so I get my result. My solved problem is that from this array I get the result of every number bring the output of substracting the next one from itself and print the result instead the original one.
[reply]

        You haven't told me how you would do it without a computer, you have just restated your problem.

        Describe the steps in English sentences. Fewer than 7 words per sentence. Only use simple steps. Prefer additional steps over more words.

[reply]
Re^3: Perl hex substraction
by ww (Archbishop) on Feb 16, 2011 at 01:25 UTC
    inkubus:

    Based on your nodes -- above and below -- I suspect you really, really need to read On asking for help and How do I post a question effectively?.

    In fact, reading the next few sentences may illuminate your quest:

    You'll get better answers here if you show that you've made some legitimate effort to solve your own problem. IOW, show us some code and explain how it fails and what error messages and warnings you see. And if you know nothing about programing, at least answer questions like Corion's -- write up a (structured) little list of the steps by which you could solve your problem with pencil and paper (for a liberal definition of "pencil and paper").

    The above answer doesn't do that. But the balance of your interactions in this thread might have gone better had you answered something like this:

    1. Subtract the second number from the first; save the difference somewhere
    2. Subtract the third number from the second; save the difference...
    3. and so on... until...
    4. Subtract ZERO from the last number and save the difference (or, phrased another way, 'simply save the last number').

    That's a simple-minded (and only partial) algorithm to address your request; translating that to code in any language is (just) a matter of matering the language.

    And we're here to help when some aspect of the language stumps you... but we're not here to write your code.

[reply]

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