策略模式（Strategy）

/*
 * 在图书销售时，根据不同类型的图书有不同的折扣，计算金额时必须区别对待，
 * 例如计算机类图书7折，英语类图书6折。应用策略模式，用C#控制台应用程序
 * 实现该设计。
 */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Strategy
{
    abstract class Strategy
    {
        public abstract double AlgorithmInterface(double Money);
    }
    class CSStrategy : Strategy
    {
          public override double AlgorithmInterface(double Money)
        {
            Console.WriteLine("计算机类书打七折。");
            return (Money*0.7);
        }
    }
    class EngStrategy : Strategy
    {
       public override double AlgorithmInterface(double Money)
        {
            Console.WriteLine("英语类书打六折。");
            return (Money * 0.6);
        }
    }
    class Context
    {
        Strategy strategy;
        public Context(Strategy strategy)
        {
            this.strategy = strategy;
        }
        public double GetResult(double Money)
        {
            return strategy.AlgorithmInterface(Money);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Context context;
            context = new Context(new CSStrategy());
            Console.WriteLine("需支付" + context.GetResult(100) + "￥");

            context = new Context(new EngStrategy());
            Console.WriteLine("需支付" + context.GetResult(100) + "￥");
        }
    }
}