update book code

eBook/examples/chapter_7/slices_forrange2.go

@@ -1,14 +1,31 @@
-package main
-import "fmt"
-
-func main() {
-    seasons := []string{"Spring", "Summer", "Autumn", "Winter"}
-    for ix, season := range seasons {
-        fmt.Printf("Season %d is: %s\n", ix, season)
-    }
-
-    var season string
-    for _, season = range seasons {
-        fmt.Printf("%s\n", season)
-    }
-}
+package main
+
+import "fmt"
+
+func main() {
+	seasons := []string{"Spring","Summer","Autumn","Winter"}
+	
+	for ix, season := range seasons {
+		fmt.Printf("Season %d is: %s\n", ix, season)
+	}
+	
+	var season string
+	for _, season = range seasons {
+		fmt.Printf("%s\n", season)
+	}
+	
+	for ix := range seasons {
+		fmt.Printf("%d ", ix)
+	}
+}
+/* Output:
+Season 0 is: Spring
+Season 1 is: Summer
+Season 2 is: Autumn
+Season 3 is: Winter
+Spring
+Summer
+Autumn
+Winter
+0 1 2 3 
+*/