Assign unique random integers in an array (C)

Question

im struggling with this so long, i can fill my array with random numbers but they are not unique. I can't spot the problem in my code :( Can you help me? Thanks

int getUniqueNumber(int *p, int i)
{
    int x,j,found;
    do
    {
        x=rand()%100000 + 1;
        found=0;
        j=0;
        while(j<=i && found==0)
        {
            if(p[i]==x)
                found=1;
            else
                j++;
        }
    } while(found==1);
    return x;
}

Well if i printf the first 10 elements here's what i get: 5 6 7 10 11 11 12 12 13 14 there are same numbers in the array.. — RoastedCode, Mar 28 '15 at 16:45
You should read [Unique random numbers in an integer array in the C programming language](http://stackoverflow.com/questions/1608181/unique-random-numbers-in-an-integer-array-in-the-c-programming-language) as well. — Arun A S, Mar 28 '15 at 16:52

score 4 · Accepted Answer · answered Mar 28 '15 at 16:46

4

p[i] == x should be p[j] == x.

answered Mar 28 '15 at 16:46

JS1

4,745
1
14
19

oh lord.. i can't believe i coudn't see that mistake all this time. Thank you so much! – RoastedCode Mar 28 '15 at 16:51

Vlad from Moscow · Answer 2 · 2015-03-28T16:53:47.923

The function can be defined the following way

int getUniqueNumber( const int *p, int i )
{
    int x, j;

    do
    {
        x = rand() % 100000 + 1;

        j = 0;
        while ( j < i && p[j] != x ) ++j;
    } while( j != i );

    return x;
}

As for your function implementation then there are a wrong condition in the loop (j <= i )

    while(j<=i && found==0)

and incorrect using of index i instead of index j

        if(p[i]==x)

Assign unique random integers in an array (C)

2 Answers2