allPrimes

allPrimes.c

/**
 * @author:     Pat Hawks
 * Created on:  Aug 28, 2014
 * Source File: allPrimes.c
 */

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

bool isPrime(int number) {
	int maxFactor = (int) sqrt(number);

	for (int possibleFactor = 2; possibleFactor <= maxFactor; ++possibleFactor) {
		if (number % possibleFactor == 0) {
			return false;
		}
	}
	return true;
}

int main() {
	for (int number=1; number > 0; ++number) {
		if (isPrime(number)) {
			printf( "%d\n", number );
		}
	}

	return 0;
}

optimizedPrimes.c

/**
 * @author:     Pat Hawks
 * Created on:  Aug 28, 2014
 * Source File: allPrimes.c
 */

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

bool isPrime(unsigned long number) {
	if (number <= 1) return false;
	if (number <= 3) return true;
	if (number % 2 == 0 || number % 3 == 0) return false;

	long maxFactor = sqrt(number);
	for (long possibleFactor = 5; possibleFactor <= maxFactor; possibleFactor += 6) {
		if (number % possibleFactor == 0 || number % (possibleFactor + 2) == 0) {
			return false;
		}
	}
	return true;
}

int main() {
	const unsigned long max = (1l<<34)-1;
	for (unsigned long number=1; number <= max; ++number) {
		if (isPrime(number)) {
			printf("%lu\n", number);
		}
	}
	return 0;
}