basic-is-prime.c

#include <math.h>
#include <stdbool.h>
#include <stdio.h>

#define BOOLEAN_FEEDBACK(boolean) ((boolean) ? "yes" : "no")

bool is_prime_clever(unsigned int number);
bool is_prime_naive(unsigned int number);

int main() {
  unsigned int non_prime_number = 2048;
  unsigned int prime_number = 2147483647;

  printf("%d prime [clever]: %s\n", prime_number, BOOLEAN_FEEDBACK(is_prime_clever(prime_number)));
  printf("%d prime [naive]:  %s\n", prime_number, BOOLEAN_FEEDBACK(is_prime_naive(prime_number)));
  printf("%d prime [clever]: %s\n", non_prime_number, BOOLEAN_FEEDBACK(is_prime_clever(non_prime_number)));
  printf("%d prime [naive]:  %s\n", non_prime_number, BOOLEAN_FEEDBACK(is_prime_naive(non_prime_number)));

  return 0;
}

bool is_prime_clever(unsigned int number) {
  for (unsigned int a = 2, b = sqrt(number); a < b; a++) {
    if ((number % a) == 0) {
      return false;
    }
  }

  return true;
}

bool is_prime_naive(unsigned int number) {
  for (unsigned int a = 2, b = (number - 1); a < b; a++) {
    if ((number % a) == 0) {
      return false;
    }
  }

  return true;
}