fix: coding style and file format for chapter 10.

eBook/exercises/chapter_10/rectangle.go

@@ -1,28 +1,29 @@
-// rectangle.go
-package main
-
-import "fmt"
-
-type Rectangle struct {
-    length, width int
-}
-
-func (r *Rectangle) Area() int {
-    return r.length * r.width
-}
-
-func (r *Rectangle) Perimeter() int {
-    return 2* (r.length + r.width)
-}
-
-func main() {
-    r1 := Rectangle{4, 3}
-    fmt.Println("Rectangle is: ", r1)
-    fmt.Println("Rectangle area is: ", r1.Area())
-    fmt.Println("Rectangle perimeter is: ", r1.Perimeter())
-}
-/* Output:
-Rectangle is:  {4 3}
-Rectangle area is:  12
-Rectangle perimeter is:  14
-*/
+// rectangle.go
+package main
+
+import "fmt"
+
+type Rectangle struct {
+	length, width int
+}
+
+func (r *Rectangle) Area() int {
+	return r.length * r.width
+}
+
+func (r *Rectangle) Perimeter() int {
+	return 2 * (r.length + r.width)
+}
+
+func main() {
+	r1 := Rectangle{4, 3}
+	fmt.Println("Rectangle is: ", r1)
+	fmt.Println("Rectangle area is: ", r1.Area())
+	fmt.Println("Rectangle perimeter is: ", r1.Perimeter())
+}
+
+/* Output:
+Rectangle is:  {4 3}
+Rectangle area is:  12
+Rectangle perimeter is:  14
+*/