使用C#写一个背包售卖小系统

using System;
using System.Collections;

namespace 背包管理器
{
    class BagManager
    {
        public ArrayList items;
        private int money;
        public BagManager(int money)
        {
            this.money = money;
            items = new ArrayList();
        }
        public void BuyItem(Item item)
        {
            if(item .num <0||item.money <0)
            {
                Console.WriteLine("请输入正确的物品信息");
                return;
            }
            if(money item.num)
                    {
                        num = item.num;
                        (items[i] as Item).num -= num;
                    }
                   else
                    {
                        //2.我有的比需要的少
                        num = (items[i] as Item).num; 
                        items.RemoveAt(i);
                    }
                    int sellMoney = (int)(money * num * 0.8f);
                    this.money += sellMoney;
                    Console.WriteLine("卖了{0}{1}赚了{2}元钱", name, num, sellMoney);
                    Console.WriteLine("目前剩余{0}元钱", this.money);
                    return;
                }
            }
        }
        public void SellItem(int id,int num=1)
        {
            //直接调用上面写好的方法
            //直接构造一个Item类 把ID和数量两个关键信息设置了即可
            Item item = new Item(id,num);
            SellItem(item);
        }
        public void ShowInfo()
        {
            Item item;
            for (int i = 0; i < items.Count ; i++)
            {
                item = items[i] as Item;
                Console.WriteLine("有{0}{1}个", item.name, item.num);
            }
            Console.WriteLine("当前拥有{1}元钱", this.money);
        }
    }
    class Item
    {
        public int id;
        public int money;
        public string name;
        public int num;
        public Item (int id ,int num)
        {
            this.id = id;
            this.num = num;
        }
        public Item (int id ,int money,string name,int num)
        {
            this.id = id;
            this.money = money;
            this.name = name;
            this.num = num;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            BagManager bag = new BagManager(9999);
            Item i1 = new Item(1, 10, "红药", 10);
            Item i2 = new Item(2, 20, "蓝宝石", 5);
            Item i3 = new Item(3, 999, "黑切", 1);

            bag.BuyItem(i1);
            bag.BuyItem(i2);
            bag.BuyItem(i3);
            bag.SellItem(i1);
            bag.SellItem(2, 6);
        }
    }
}