高手` -帮小弟我看看这个小疑点

高手`- -帮我看看这个小问题
using System;
using System.Collections.Generic;
using System.Text;

namespace book
{
    class Program
    {
        static void Main(string[] args)
        {
            int money;
            string vip;
            Console.Write("请输入购书的金额：");
            money = int.Parse(Console.ReadLine());
            Console.Write("请输入是否是会员：");
            vip = Console.ReadLine();


            if (money>=100&&vip!="是")
            {
                Console.Write("享受9折优惠");
                
            }
            else if (vip=="是"&&money=<200)
            {
                Console.Write("享受8折");
                
            }
            else if (money > 200 && vip == "是")
            {
                Console.Write("享受7.5折");

            }
            else
            {
                Console.Write("没有优惠");
            }
            Console.ReadLine();
        }
    }
}

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