update book code

eBook/exercises/chapter_6/factorial.go

@@ -0,0 +1,34 @@
+// factorial.go
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	for i := uint64(0); i < uint64(30); i++ {
+		fmt.Printf("Factorial of %d is %d\n", i, Factorial(i))
+	}
+}
+
+/* unnamed return variables:
+func Factorial(n uint64) uint64 {
+	if n > 0 {
+		return n * Factorial(n-1)
+	}
+	return 1
+}
+*/
+
+// named return variables:
+func Factorial(n uint64) (fac uint64) {
+	fac = 1
+	if n > 0 {
+		fac = n * Factorial(n-1)
+		return
+	}
+	return
+}
+
+// int: correct results till 12!
+// uint64: correct results till 21!