PrimeNumber

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int feltes(int n);
int prime(int n);
int main(void) {
  int i, j, P[20], n, ans;
  for (i = 0; i < 20; i++)
    P[i] = 0;
  puts("feltes:");
  for (i = 2; i < 100; i++)
    if (feltes(i)) printf("%d\n", i);
  puts("prime:");
  srand((unsigned) time(NULL));
  for (i = 0; i < 20; i++) {
    do {
      n = (int) ((rand() / ((double) RAND_MAX + 1.)) * 100) + 1;
      ans = prime(n);
      if (ans != 1) continue;
      for (j = 0; j < i; j++)
        if (P[j] == n) goto cont;
      P[i] = n;
      break;
      cont: continue;
    } while (1);
    printf("%d\n", P[i]);
  }
  return 0;
}
int feltes(int n) {
  int i, j;
  unsigned long long rui;
  if (n < 2) return 0;
  if (n == 2) return 1;
  for (i = 2; i < n - 1; i++) {
    rui = i;
    for (j = 1; j < n - 1; j++) {
      rui *= i;
      if (rui < 0) return 0;
    }
    if (rui % n != 1) {
      return 0;
    } else {
      return 1;
    }
  }
  return 0;
}
int prime(int n) {
  int i;
  if (n < 2) return 0;
  if (n == 2) return 1;
  for (i = 2; i * i <= n; i++)
    if (n % i == 0) return 0;
  return 1;
}