Shuffle array not working properly

Question

I'm currently using this function to muddle up all items of an array :

void shuffleArray(int *array)
{
    int index;
    int buffer
    int randomIndex;
    srand((int)time(NULL));
    //SIZE is my tab's length
    for(index = 0; index < SIZE - 1; index++)
    {
        randomIndex = (index + rand() / (RAND_MAX / SIZE - index) + 1));
        buffer = array[randomIndex];
        array[randomIndex] = array[index];
        array[index] = buffer;
    }
}

But I've a problem: The first value of my array is always the same as a function of current time.

I'm lost, if you can show me the right way..

What exactly do you mean? Do you mean that the sequence of random incices is the same all time? — Codor, Dec 23 '14 at 08:09
No, only my the first item ! For exemple array : 1 - 2 - 3 - 4 - 5 would be after a shuffle : 2 - 4 - 3 - 1 - 5. 2 would be all the time the first element during a few minutes — , Dec 23 '14 at 08:14
http://stackoverflow.com/questions/7343833/srand-why-call-only-once This might help you — Ashwani, Dec 23 '14 at 08:14

score 1 · Accepted Answer · edited May 23 '17 at 10:33

1

srand() gets you the same random number once for a program so thats the problem

srand() — why call it only once?

This can help

edited May 23 '17 at 10:33

Community

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answered Dec 23 '14 at 09:01

Aditya Kiran

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I've put srand in my main, same result :/ But ty for the advice – Dec 23 '14 at 09:05
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Finally, this worked fine (i've take a lot of time to understand this) : struct timeval t1; gettimeofday(&t1, NULL); srand((int)(t1.tv_usec * t1.tv_sec)); Thanks all, +1 – Dec 23 '14 at 09:27
@AdrienWeidemann: That (using both seconds and microseconds to create a seed value) works after a fashion, though it excludes prime numbers from the list of seed values, but it is still an abuse of the way you're supposed/intended to use `srand()` if you call it multiple times. – Jonathan Leffler Dec 23 '14 at 15:34

Shuffle array not working properly

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