Question

I have written the following code to generate random numbers in C.

int main (int argc, char *argv[])
{
    unsigned int iseed = (unsigned int)time(NULL);
    srand (iseed);

    /* Generate random number*/
    int i;
    for (i = 0; i < 1; i++)
    {
        printf ("Random[%d]= %u\n", i, rand ());
    }
    return 0;
}

The output gives me a 10 digit random number, how can I change the number of digits printed in the output?

Answer 1

rand() gives you a number between 0 and RAND_MAX, which may be a large number.

If you want to get a uniform sample in the range [0, N), you need to divide the range into regions:

int my_max = (RAND_MAX / N) * N;

int result;

while ((result = rand()) >= my_max) { } // #1

return result % N;

The condition on line #1 should be met only very rarely, but we need to re-roll in the case where the result doesn’t lie inside a range that is a multiple of N to avoid bias against high results.