// 定義一個(gè)抽象基類
abstract class Animal
{
    public abstract void MakeSound();
}

// 派生類實(shí)現(xiàn)具體行為
class Dog : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Woof!");
    }
}

class Cat : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Meow!");
    }
}

// 使用多態(tài)代替條件語(yǔ)句
Animal myAnimal = new Dog();
myAnimal.MakeSound(); // 輸出: Woof!

myAnimal = new Cat();
myAnimal.MakeSound(); // 輸出: Meow!

public string GetDayOfWeek(int dayNumber)
{
    var days = new Dictionary<int, string>
    {
        { 1, "星期一" },
        { 2, "星期二" },
        { 3, "星期三" },
        { 4, "星期四" },
        { 5, "星期五" },
        { 6, "星期六" },
        { 7, "星期日" }
    };

    return days.TryGetValue(dayNumber, out var day) ? day : "無(wú)效的天數(shù)";
}

string name = null;

// 使用空合并運(yùn)算符（??）提供默認(rèn)值
string displayName = name ?? "Guest";
Console.WriteLine(displayName); // 輸出: Guest

// 使用空條件運(yùn)算符（?.）避免空引用異常
int? length = name?.Length;
Console.WriteLine(length ?? 0); // 輸出: 0

int age = 20;

// 使用三元運(yùn)算符代替 if-else
string status = age >= 18 ? "Adult" : "Minor";
Console.WriteLine(status); // 輸出: Adult

// 策略接口
public interface IDiscountStrategy
{
    double CalculateDiscount(double amount);
}

// 幾個(gè)策略實(shí)現(xiàn)
public class NoDiscount : IDiscountStrategy
{
    public double CalculateDiscount(double amount) => 0;
}

public class FivePercentDiscount : IDiscountStrategy
{
    public double CalculateDiscount(double amount) => amount * 0.05;
}

public class TenPercentDiscount : IDiscountStrategy
{
    public double CalculateDiscount(double amount) => amount * 0.10;
}

// 上下文
public class DiscountContext
{
    private IDiscountStrategy _strategy;

    public DiscountContext(IDiscountStrategy strategy)
    {
        _strategy = strategy;
    }

    public double GetDiscount(double amount)
    {
        return _strategy.CalculateDiscount(amount);
    }
}

// 使用示例
var context = new DiscountContext(new TenPercentDiscount());
var discount = context.GetDiscount(150); // 15

var numbers = new List<int> { 1, 2, 3, 4, 5, 6 };

// 使用 LINQ 過(guò)濾偶數(shù)
var evenNumbers = numbers.Where(n => n % 2 == 0).ToList();

Console.WriteLine(string.Join(", ", evenNumbers)); // 輸出: 2, 4, 6

// （擴(kuò)展應(yīng)用）
string message = input switch {
    int n when n < 0 => "負(fù)數(shù)",
    int n when n == 0 => "零",
    int n when n > 0 => "正數(shù)",
    _ => "未知"
};
Console.WriteLine(message);

// 定義一個(gè)委托
Func<int, bool> isEven = x => x % 2 == 0;

// 使用委托代替條件語(yǔ)句
Console.WriteLine(isEven(4) ? "Even" : "Odd"); // 輸出: Even
Console.WriteLine(isEven(3) ? "Even" : "Odd"); // 輸出: Odd

public void ProcessOrder(Order order)
{
    if (order == null) return;
    if (order.Items.Count <= 0) return;

    // 處理訂單邏輯
}