My C++ Homework...Simple Question

This is a discussion on My C++ Homework...Simple Question within the C++ Programming forums, part of the General Programming Boards category; I need to draw 8 random numbers (from 1 to 4). The numbers can only repeat once. I need there ...

  1. #1
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    My C++ Homework...Simple Question

    I need to draw 8 random numbers (from 1 to 4). The numbers can only repeat once. I need there to be two 1s, two 2s, two 3s, and two 4s in random order. I need them put into an array.

    Example Output: 1,3,4,2,4,1,3,2 or 3,1,1,4,3,2,2,4 (I'm sure you get the idea!)

    It would now equal:

    Code:
    intNumbers[8] = {1,3,4,2,4,1,3,2};
    This is a small piece of a bigger project, so I not just on here asking for answers. I really need help with this one. I've been staring at the same 10 lines for several hours now.

    Thanks in advance for any help!
    Tin

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    You can put 1,1,2,2,3,3,4,4 into a <vector> and then call random_shuffle() on the vector. You can then copy() the elements of the vector to your array, although you might consider using a <vector> instead of an array to start with--then you wouldn't need to copy the <vector> to the array.

    random_shuffle() is in <algorithm>.
    Last edited by 7stud; 02-08-2006 at 10:20 PM.

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    If you have to use the C style array, random_shuffle will work with that also:

    std::random_shuffle(intNumbers, intNumbers + 8);

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    Quote Originally Posted by Daved
    If you have to use the C style array, random_shuffle will work with that also:

    std::random_shuffle(intNumbers, intNumbers + 8);
    Darn it.

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    Thanks a million. Worked like a charm!

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    Just so you know, you need to use srand(time(0)) to seed rand(), which is used by random_shuffle(). Otherwise, you will get the exact same sequence every time you run your program--try it.

    time() is in <ctime>

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    Luckily I already had that in my code. If I didn't, I would've been stumped. Thanks again!

  8. #8
    ZuK
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    Quote Originally Posted by 7stud
    Just so you know, you need to use srand(time(0)) to seed rand(), which is used by random_shuffle(). Otherwise, you will get the exact same sequence every time you run your program--try it.
    The implementation of the STL that I use ( g++ ) dosen't make use of the normal rand(), srand() c-functions. It uses an internal random generator that cannot be seeded.
    but it's simple to provide one if needed

    Code:
    struct randomgenerator {
       int operator()( int range ) {
           static int seeded = 0;
           if ( ! seeded ) {
               srand( time(0));
               ++seeded;
           }
           return rand() % range;
       }
    };
    use it this way:
    Code:
        randomgenerator random;
    
        random_shuffle( intNumbers, intNumbers + 8, random );
    Kurt

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    functor! Functor! I see you!

    struct? <shudder>

  10. #10
    ZuK
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    Quote Originally Posted by 7stud
    functor! Functor! I see you!

    struct? <shudder>
    What's wrong with that struct. There is nothing to be hidden or protected ?
    Kurt

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