more cleanup, more c examples

1 files changed, 50 insertions, 0 deletions

diff --git a/sumofprimes.c b/sumofprimes.c
new file mode 100644
index 0000000..90e0bbb
--- /dev/null
+++ b/sumofprimes.c
@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+// The number to find primes up to
+int n = 2000000;
+
+// The number of primes in the primes array
+int s = 0;
+
+int *listPrimes(int num){
+	int i;
+	int *primes;
+	int *sieve = (int *) malloc(num * sizeof(int));
+	//initialize to all 1s (except 0 and 1 which are not prime)
+	for(i = 2; i < num; i++)
+		sieve[i] = 1;
+	for(i = 2; i < ceil(sqrt(num)); i++){
+		if(sieve[i] ==  1){
+			int j = i * i;
+			while(j < num){
+				sieve[j] = 0;
+				j += i;
+			}
+		}
+	}
+	
+	//now check which were prime
+	primes = (int *) malloc(sizeof(int));
+	for(i = 2; i < num; i++){
+		if(sieve[i]){
+			primes[s] = i;
+			s++;
+			primes = (int *) realloc (primes, (s + 1) * sizeof(int));
+		}
+	}
+
+	return primes;
+}
+
+int main(){
+	int *p = listPrimes(n);
+    long long sum = 0;
+    int len = s;
+    for(int i = 0; i < s; i++){
+        sum += p[i];
+    }
+	printf("%ld\n", sum);
+	return 0;
+}