diff --git a/main.c b/main.c
index 71d81af..4baddfb 100644
--- a/main.c
+++ b/main.c
@@ -13,11 +13,11 @@
 
 struct _virtual_table
 {
-    VIRTUAL void (*area)(void *self, void *parent);
+    VIRTUAL double (*area)(void *self, void *parent);
     VIRTUAL void (*draw)(void *self, void *parent);
 };
 
-void virtual_area(void *self, void *parent)
+double virtual_area(void *self, void *parent)
 {
     ASSERT_CALL_VIRTUAL_METHOD();
 }
@@ -44,10 +44,12 @@ struct _shape
     struct _virtual_table vtb;
 };
 
-void shape_area(void *self, void *parent)
+double shape_area(void *self, void *parent)
 {
+    double area = 0;
     struct _shape *pthis = (struct _shape *)parent;
-    pthis->vtb.area(self, NULL);
+    area = pthis->vtb.area(self, NULL);
+    return area;
 }
 
 void shape_draw(void *self, void *parent)
@@ -56,7 +58,7 @@ void shape_draw(void *self, void *parent)
     pthis->vtb.draw(self, NULL);
 }
 
-PRIVATE void _shape_area(void *self, void *parent)
+PRIVATE double _shape_area(void *self, void *parent)
 {
     ASSERT_CALL_VIRTUAL_METHOD();
 }
@@ -74,7 +76,7 @@ struct _shape *shape_new(void)
         return NULL;
     }
     static struct _virtual_table vtb = {
-        .area = (void (*)(void *self, void *parent))_shape_area, 
+        .area = (double (*)(void *self, void *parent))_shape_area, 
         .draw = (void (*)(void *self, void *parent))_shape_draw
     };
     shape->vtb = vtb;
@@ -108,9 +110,11 @@ struct _rect
     // void (*draw)(void *self);
 };
 
-void rect_area(struct _rect *self, void *parent)
+double rect_area(struct _rect *self, void *parent)
 {
-    printf("rect area = %0.2f\n", self->width * self->height);
+    double area = self->width * self->height;
+    printf("rect area = %0.2f\n", area);
+    return area;
 }
 
 void rect_draw(struct _rect *self, void *parent)
@@ -129,7 +133,7 @@ struct _rect *rect_new(double width, double height)
     rect->height = height;
 
     static struct _virtual_table vtb = {
-        .area = (void (*)(void *self, void *parent))rect_area,
+        .area = (double (*)(void *self, void *parent))rect_area,
         .draw = (void (*)(void *self, void *parent))rect_draw
     };
 
@@ -155,9 +159,11 @@ struct _circle
     // void (*draw)(void *self);
 };
 
-void circle_area(struct _circle *self, void *parent)
+double circle_area(struct _circle *self, void *parent)
 {
-    printf("circle area = %0.2f\n", 3.14 * self->radius * self->radius);
+    double area = 3.14 * self->radius * self->radius;
+    printf("circle area = %0.2f\n", area);
+    return area;
 }
 void circle_draw(struct _circle *self, void *parent)
 {
@@ -174,7 +180,7 @@ struct _circle *circle_new(double radius)
     circle->radius = radius;
 
     static struct _virtual_table vtb = {
-        .area = (void (*)(void *self, void *parent))circle_area,
+        .area = (double (*)(void *self, void *parent))circle_area,
         .draw = (void (*)(void *self, void *parent))circle_draw,
     };
 
@@ -183,45 +189,61 @@ struct _circle *circle_new(double radius)
     return circle;
 }
 
-#if 0
-struct _cube
+struct _copper_cash
 {
-    // 继承自 struct _shape
-    struct _rect;
-    
-    // attibute
-    double length;
+    struct _shape shape;
+    struct _rect *rect;
+    struct _circle *circle;
+
+    double price;
 };
 
-void cube_area(struct _cube *self)
+double copper_cash_area(struct _copper_cash *self, void *parent)
 {
-    printf("cube area = %0.2f\n", self->length * self->length * self->length);
+    double circle_area = self->circle->shape.vtb.area(self->circle, self->circle);
+    double rect_area = self->rect->shape.vtb.area(self->rect, self->rect);
+    double area = circle_area - rect_area;
+
+    printf("copper cash area = %0.2f\n", circle_area - rect_area);
+    return area;
 }
 
-void cube_draw(struct _cube *self)
+void copper_cash_draw(struct _copper_cash *self, void *parent)
 {
-    printf("cube draw\n");
+    printf("copper cash draw\n");
 }
 
-struct _cube* cube_new(double length)
+
+struct _copper_cash *copper_cash_new(double width, double height, double radius)
 {
-    struct _cube *cube = calloc(1, sizeof(struct _cube));
-    if (cube == NULL)
+    struct _copper_cash *cc = calloc(1, sizeof(struct _copper_cash));
+    if (cc == NULL)
     {
         return NULL;
     }
-    cube->length = length;
+
+    struct _rect *rect = rect_new(width, height);
+    if(rect == NULL)
+    {
+        return NULL;
+    }
+    cc->rect = rect;
+
+    struct _circle *circle = circle_new(radius);
+    if (circle == NULL)
+    {
+        return NULL;
+    }
+    cc->circle = circle;
+    cc->price = 100;
 
     static struct _virtual_table vtb = {
-        .area = (void (*)(void *self))cube_area,
-        .draw = (void (*)(void *self))cube_draw,
+        .area = (double (*)(void *self, void *parent))copper_cash_area,
+        .draw = (void (*)(void *self, void *parent))copper_cash_draw,
     };
-
-    cube->vtb = vtb;
-    return cube;
+    cc->shape.vtb = vtb;
+    return cc;
 }
-#endif
-
 
 int main(int argc, char *argv[])
 {
@@ -233,14 +255,14 @@ int main(int argc, char *argv[])
     circle_area(circle, circle);
     circle_draw(circle, circle);
 
-    printf("------------------------------\n");
+    printf("----- rect & circle -----\n");
     shape_area(rect, &rect->shape);
     shape_draw(rect, &rect->shape);
 
     shape_area(circle, &circle->shape);
     shape_draw(circle, &circle->shape);
 
-    printf("------------------------------\n");
+    printf("----- [2] rect & circle -----\n");
     struct _rect *rect2 = (struct _rect *)rect_new(2, 3);
     shape_area(rect2, &rect2->shape);
     shape_draw(rect2, &rect2->shape);
@@ -249,10 +271,15 @@ int main(int argc, char *argv[])
     shape_area(circle2, &circle->shape);
     shape_draw(circle2, &circle->shape);
 
-    printf("------------------------------\n");
-    struct _shape *shape = shape_new();
-    shape_area(shape, shape);
-    shape_draw(shape, shape);
+    // printf("----- [2] shape -----\n");
+    // struct _shape *shape = shape_new();
+    // shape_area(shape, shape);
+    // shape_draw(shape, shape);
+
+    printf("----- copper_cash -----\n");
+    struct _copper_cash *cc = copper_cash_new(2, 2, 4);
+    shape_area(cc, &cc->shape);
+    shape_draw(cc, &cc->shape);
 
     return 0;
 }