package main

import (
	"fmt"
	"math"
)

type Shape interface {
	Area() float64
	Perimeter() float64
}

type Rectangle struct {
	Width  float64
	Height float64
}

type Circle struct {
	Radius float64
}

func (r Rectangle) Area() float64 {
	return ____
}

func (r Rectangle) Perimeter() float64 {
	return ____
}

func (c Circle) Area() float64 {
	return math.Pi * ____ * ____
}

func (c Circle) Perimeter() float64 {
	return 2 * math.Pi * ____
}

type ShapePrinter interface {
	PrintInfo()
}

func (r Rectangle) PrintInfo() {
	fmt.Printf("矩形 - 宽: %.2f, 高: %.2f\n", ____, ____)
}

func (c Circle) PrintInfo() {
	fmt.Printf("圆形 - 半径: %.2f\n", ____)
}

func exercise1() float64 {
	fmt.Println("=== 练习1：矩形接口实现 ===")

	rect := Rectangle{Width: 10, Height: 5}

	area := ____
	perimeter := ____

	fmt.Printf("矩形面积: %.2f, 周长: %.2f\n", area, perimeter)

	return ____
}

func exercise2() string {
	fmt.Println("=== 练习2：圆形接口实现 ===")

	circle := Circle{Radius: 7}

	area := ____
	info := fmt.Sprintf("圆形面积: %.2f", area)

	fmt.Println(____)

	return ____
}

func exercise3() string {
	fmt.Println("=== 练习3：多态 ===")

	// 定义一个Shape类型的变量，分别指向Rectangle和Circle
	var s Shape

	s = ____
	fmt.Printf("形状类型: %T, 面积: %.2f\n", s, s.____())

	s = ____
	fmt.Printf("形状类型: %T, 面积: %.2f\n", s, s.____())

	return "多态演示完成"
}

func exercise4() interface{} {
	fmt.Println("=== 练习4：空接口 ===")

	// 空接口可以持有任何类型
	var data interface{}

	data = ____
	fmt.Printf("数据: %v, 类型: %T\n", data, data)

	data = ____
	fmt.Printf("数据: %v, 类型: %T\n", data, data)

	data = ____
	fmt.Printf("数据: %v, 类型: %T\n", data, data)

	return ____
}

type Animal interface {
	Sound() string
}

type Dog struct{}

func (d Dog) Sound() string {
	return "汪汪"
}

type Cat struct{}

func (c Cat) Sound() string {
	return ____
}

func exercise5() string {
	fmt.Println("=== 练习5：接口组合与使用 ===")

	// 创建Animal切片，包含不同的动物
	animals := []Animal{____, ____}

	for _, animal := range ____ {
		fmt.Printf("动物发出的声音: %s\n", animal.____())
	}

	return "动物接口演示完成"
}

func main() {
	fmt.Println("=== 接口 练习 ===\n")

	result1 := exercise1()
	fmt.Printf("练习1结果: %.2f\n", result1)

	result2 := exercise2()
	fmt.Printf("练习2结果: %s\n", result2)

	result3 := exercise3()
	fmt.Printf("练习3结果: %s\n", result3)

	result4 := exercise4()
	fmt.Printf("练习4结果: %v (类型: %T)\n", result4, result4)

	result5 := exercise5()
	fmt.Printf("练习5结果: %s\n", result5)
}