added fibonacci source and executable

src/5_p_c_fibonacci.c

@@ -0,0 +1,43 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+/* declarations */
+int sum(int n);
+int fib(int n);
+
+int main() {
+	int n;
+
+	printf("Please enter n: ");
+	scanf("%d", &n);
+	printf("fib(%d) = %d\nsum(%d) = %d\n", n, fib(n), n, sum(n));
+
+	return 0;
+}
+
+int sum(int n) {
+	int i, sum = 0;
+
+	for (i = 1; i <= n; i++) {
+		sum += i;
+	}
+
+	return sum;
+}
+
+int fib(int n) {
+	if (n >= 2) {
+		return fib(n-1) + fib(n-1);
+	}
+	else if (n == 1) {
+		return 1;
+	}
+	else if (n == 0) {
+		return 0;
+	}
+	else {
+		fprintf(stderr, "Invalid parameter: %d", n);
+		exit(-1);
+	}
+}
+