using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace 密码登入
{
    class Program
    {
        static void Main(string[] args)
        {
            string id;
            string useid;
           //string usepw="";
            int count = 0;
            Console.Write("请注册帐号：\n");
            id = Console.ReadLine();
            Console.Write("请设定密码:\n");
            string pw =Console.ReadLine();
            Console.Clear();
            while (count<=3)
            {
                while (true)
                {
                    
                    Console.Write("请输入你的帐号：\n");
                    useid = Console.ReadLine();
                    Console.Write("请输入密码：\n");
                    ConsoleKeyInfo usepw = Console.ReadKey(true);
                    if (usepw.Key== ConsoleKey.Enter) break;
                    Console.Write("*");
                    usepw = usepw + pw.KeyChar.ToString();
                    if (useid == id && usepw.KeyChar.ToString() == pw)
                    {
                        Console.Write("登入成功！！！");
                    }
                    else
                    {
                        Console.Write("请重新登入：\n");
                        count++;
                        if (count%3==0)
                            break;
                    }
                    Console.Clear();
                    Console.Write("登入失败！！！");
                    Console.ReadKey();
                }
            }
        }
    }
}

pw.KeyChar
pw是字符串，不包含KeyChar的定义

usepw = usepw + pw.KeyChar.ToString();
pw里面没有KeyChar这东西

要怎么改啊

static void Main(string[] args)
        {
            string id;
            string useid;
            //string usepw="";
            int count = 0;
            Console.Write("请注册帐号：\n");
            id = Console.ReadLine();
            Console.Write("请设定密码:\n");
            string pw = Console.ReadLine();
            Console.Clear();
            while (count <= 3)
            {
                Console.Write("请输入你的帐号：\n");
                useid = Console.ReadLine();
                Console.Write("请输入密码：\n");
                string inputPass = string.Empty;
                while (true)
                {
                    ConsoleKeyInfo usepw = Console.ReadKey(true);
                    if (usepw.Key == ConsoleKey.Enter) break;
                    Console.Write("*");
                    inputPass += usepw.KeyChar.ToString();
                }
                if (useid == id && inputPass == pw)
                {
                    Console.Write("登入成功！！！");
                    return;
                }
                else
                {
                    Console.Write("请重新登入：\n");
                    count++;
                }
            }
            Console.Clear();
            Console.Write("登入失败！！！");
            Console.ReadKey();
}