update book code

eBook/exercises/chapter_6/fibonacci2.go

@@ -0,0 +1,24 @@
+package main
+
+import "fmt"
+
+func main() {
+	pos := 4
+	result, pos := fibonacci(pos) 
+	fmt.Printf("the %d-th fibonacci number is: %d\n", pos, result)
+	pos = 10
+	result, pos = fibonacci(pos) 
+	fmt.Printf("the %d-th fibonacci number is: %d\n", pos, result)
+}
+
+func fibonacci(n int) (val, pos int) {
+	if n <= 1 {
+		val = 1
+	} else {
+		v1, _ := fibonacci(n-1)
+		v2, _ := fibonacci(n-2)
+		val =  v1 + v2
+	}
+	pos = n
+	return
+}