random with /dev/urandom

random.c

#include <stdio.h> 
#include <unistd.h> 
#include <stdlib.h> 
#include <math.h> 

int main (int argc, char *argv[]) 
{ 
    FILE *urandom; 
    unsigned int seed; 

    urandom = fopen ("/dev/urandom", "r"); 
    if (urandom == NULL) { 
        fprintf (stderr, "Cannot open /dev/urandom!\n"); 
        exit (1); 
    } 
    fread (&seed, sizeof (seed), 1, urandom); 

    srand (seed); /* seed the pseudo-random number generator */ 

    printf ("Random number from 1 to 100: %d\n", (int) floor (rand() * 100.0 / ((double) RAND_MAX + 1) )+ 1); 
    exit (0); 
}