Birthdays (Aliens Question)

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

double get_birthdays(int n);

int cmpfunc (const void * a, const void * b);

int main(int argc, char **argv) {
  for(int n = 366; n < 500; n++){
    printf("%f\n", get_birthdays(n));
  }
}

int cmpfunc (const void * a, const void * b) {
   return ( *(int*)a - *(int*)b );
}

double get_birthdays(int n) {
  srand(time(NULL));
  int birthdays[25];
  int b;
  int count = 0;
  for(int i = 0; i < 10000; i++){
    b = 0;
    for(int j = 0; j < 25; j++){
      birthdays[j] = rand() % n;
    }
    qsort(birthdays, 25, sizeof(int), cmpfunc);
    for(int j = 0; j < 24; j++){
      if(birthdays[j] == birthdays[j+1]){
        b = 1;
      }
    }
    if(b){
      count++;
    }
  }
  return ((double) count)/10000.0;
}