Add all the A tasks

Task/Averages-Arithmetic-mean/C/averages-arithmetic-mean.c

@@ -0,0 +1,24 @@
+#include <stdio.h>
+
+double mean(double *v, int len)
+{
+	double sum = 0;
+	int i;
+	for (i = 0; i < len; i++)
+		sum += v[i];
+	return sum / len;
+}
+
+int main(void)
+{
+	double v[] = {1, 2, 2.718, 3, 3.142};
+	int i, len;
+	for (len = 5; len >= 0; len--) {
+		printf("mean[");
+		for (i = 0; i < len; i++)
+			printf(i ? ", %g" : "%g", v[i]);
+		printf("] = %g\n", mean(v, len));
+	}
+
+	return 0;
+}