Using Only Primes As Divisors in C

#include 
#include 
#include 
#include 

typedef  unsigned long long bignum;

struct primerec
 {
 bignum bn;
 struct primerec * next;
 };

void printPrime(bignum bn)
 {
 static char buf[1000];

 sprintf(buf, "%ull", bn);
 buf[strlen(buf) - 2] = '\0';
 printf("%s\n", buf);
 }

void freeList(struct primerec *head)
 {
 struct primerec *thisPrime = head;
 while(1)
  {
  struct primerec *nextPrime = thisPrime->next;
  free(thisPrime);
  if(nextPrime == NULL)
   break;
  else
   thisPrime = nextPrime;
  }
 }

void findPrimes(bignum topCandidate)
 {
 struct primerec *firstPrime = malloc(sizeof(struct primerec));
 assert(firstPrime != NULL);
 struct primerec *latestPrime = firstPrime;
 firstPrime->bn = 2;
 firstPrime->next=NULL;
 bignum candidate = 2;
 while(candidate <= topCandidate)   
{   
struct primerec *thisPrime = firstPrime;   
int prime = 1;   
while(thisPrime->bn * thisPrime->bn <= candidate)    
{    if(candidate % thisPrime->bn == 0)
    {
    prime = 0;
    break;
    }
   thisPrime = thisPrime->next;
   }
  if(prime)
   {
   printPrime(candidate);
   latestPrime->next = malloc(sizeof(struct primerec));
   assert(latestPrime->next != NULL);
   latestPrime = latestPrime->next;
   latestPrime->bn = candidate;
   latestPrime->next = NULL;
   }
  candidate++;
  }
 freeList(firstPrime);
 }

int main(int argc, char *argv[])
 {
 bignum topCandidate = 1000;
 if(argc > 1)
  topCandidate = atoll(argv[1]);
 findPrimes(topCandidate);
 return 0;
 }