Rand() function

This is a discussion on Rand() function within the C++ Programming forums, part of the General Programming Boards category; Hi. Im looking for a simpley way to pick randomly one of thease numbers: 1-2-3-4. I have searched on google, ...

  1. #1
    Politics&Cpp geek Da-Nuka's Avatar
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    Rand() function

    Hi.
    Im looking for a simpley way to pick randomly one of thease numbers:
    1-2-3-4.

    I have searched on google, but finds nothing but how to get a randomnumber between 0 and some stupid max-number!

  2. #2
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    Code:
    int somevariable = (rand()%4 + 1)
    rand()%X (where X is a number) gives you a number between 0 and X-1. That's why we add the +1, so you get between 1 and X.

  3. #3
    ATH0 quzah's Avatar
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    You could have always just read the FAQ entry on the subject.

    [edit]
    On an aside, did you never think to just simply add one to the number, since you know it starts at zero, and you want it to start at one? I hope you don't have to ask again when you want to generate a number starting at 2. Or 3. Or again at 4...
    [/edit]

    Quzah.
    Last edited by quzah; 12-25-2004 at 03:09 PM.
    Hope is the first step on the road to disappointment.

  4. #4
    VA National Guard The Brain's Avatar
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    To answer your next question.. you probably forgot to seed your random number generator.

    Code:
    srand(unsigned(time( ));
    This is to be done only once.
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  5. #5
    ATH0 quzah's Avatar
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    To answer your next next question, you'll need a set of parenthesis around that unsigned, like this for it to actually work:
    Code:
    srand( (unsigned) time( ) );
    Oh, and of course you'll actually have to provide a value to the time function. So you really end up with something like this:
    Code:
    srand( (unsigned) time( 0 ) );
    Or, you could have just read the FAQ as I suggested, which covers srand.

    Quzah.
    Hope is the first step on the road to disappointment.

  6. #6
    & the hat of GPL slaying Thantos's Avatar
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    Oh course since this is c++ you could be using the proper type of casting:
    Code:
    srand( static_cast<unsigned>( time(0) ) );

  7. #7
    I am the worst best coder Quantrizi's Avatar
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    Quote Originally Posted by Da-Nuka
    Hi.
    Im looking for a simpley way to pick randomly one of thease numbers:
    1-2-3-4.

    I have searched on google, but finds nothing but how to get a randomnumber between 0 and some stupid max-number!
    Then obviously you don't know what a max number is *cough* 4 is your max number for the sequent 1-2-3-4 */cough*. It's not brain surgery...and as Quzah said, the FAQ is god...

  8. #8
    Code Goddess Prelude's Avatar
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    And you can't forget that time_t isn't guaranteed to be convertible to unsigned int:
    Code:
    unsigned int random_seed()
    {
      unsigned int seed(0);
      time_t now = time(0);
      unsigned char *p = reinterpret_cast<unsigned char *>(&now);
    
      for (size_t i = 0; i < sizeof now; i++)
        seed = seed * (numeric_limits<unsigned char>::max() + 2U) + p[i];
    
      return seed;
    }
    
    ...
    
    srand(random_seed());
    My best code is written with the delete key.

  9. #9
    Politics&Cpp geek Da-Nuka's Avatar
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    Im not that noob
    Just lazy!

    All I needed was the function name... (first post)

    And I feel I gotta defend my self a little:
    I wasnt talking about 4 as the max number, if I had found ways to do that, the problem had been solved.

    The maxnumber I allways bumbed into was RAND_MAX.

    A example:
    http://www.phim.unibe.ch/comp_doc/c_...IONS/rand.html
    Last edited by Da-Nuka; 12-26-2004 at 02:25 AM.

  10. #10
    Code Goddess Prelude's Avatar
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    >Just lazy!
    That's a bad kind of lazy.

    >I wasnt talking about 4 as the max number, if I had found ways to do that, the problem had been solved.
    I don't understand. How is "get a randomnumber between 0 and some stupid max-number!" different from what you want? Unless you want a random permutation, what you've been finding is a viable solution. Give us more detail as to what you're trying to do.
    My best code is written with the delete key.

  11. #11
    Super Moderator
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    Just lazy!
    We're not here to do work for you. We're here to help you with problems. If you know how to solve the problem and are just too lazy to do it yourself, you'll quickly find the same attitude towards helping you.

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