3_digit_primes

#include <cmath>
#include <cstdio>
#include <vector>

bool is_prime(unsigned int num);
unsigned int find_bigger_prime(unsigned int num);

std::vector<unsigned int> prime_lookup = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31};

//Works only for 3 digit primes
unsigned int find_bigger_prime(unsigned int num) {
  num += 2;
  while ((!is_prime(num)) && (num < 1000)) {
    num += 2;
  }
  return num;
}

bool is_prime(unsigned int num) {
  unsigned int num_sqrt = (unsigned int)sqrt(num);
  for (unsigned int i : prime_lookup) {
    if (i > num_sqrt) {
      break;
    }
    if ((num % i) == 0) {
      return false;
    }
  }
  return true;
}

int main(void) {
  unsigned int prime = 101;
  while (prime < 1000) {
    printf("%u ", prime);
    prime = find_bigger_prime(prime);
  }
  putchar('\n');
  return 0;
}