Merge pull request #59 from danielgrimshaw/master

Add Sieve of Eratosthenes

primes.c

@@ -0,0 +1,46 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+void primes(bool * primeList, int len) {
+	int i, j;
+
+	// Initiallize the list
+	for (i = 0; i < len; i++) {
+		primeList[i] = true;
+	}
+	primeList[0] = false; // 0 is not prime
+	primeList[1] = false; // 1 is not prime
+
+	for (i = 0; i < len; i++) {
+		if (primeList[i] == true) {
+			for (j = i*i; j < len; j = j+i) {
+				primeList[j] = false;
+			}
+		}
+	}
+}
+
+int main(void) {
+	int size, i;
+	bool * list;
+
+	// Ask for the largest value to check primeness
+	printf("Maximum value: ");
+	scanf("%d", &size);
+
+	// Allocate list to act as prime mask
+	list = malloc(sizeof(bool) * size);
+
+	// Populate list
+	primes(list, size);
+
+	// Print prime numbers
+	for (i = 0; i < size; i++) {
+		if (list[i] == true) {
+			printf("%d\n", i);
+		}
+	}
+
+	return 0;
+}