虚心请教C#sql连接,未将对象引用设置到对象的实例刚学代码有点乱,别见怪

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

namespace ConsoleApplication1
{
    class DBOperation
    {
        private static string conn = "Data Source=.;Initial Catalog=qq;Integrated Security=True";
        //User ID=sa;Password=123456";如果Password为空，可以不写
         public static SqlConnection con = new SqlConnection(conn);
           string strMsg="";
           #region 异常处理
           public void Conn()
           {
               try
               {
                   //打开数据库
                   con.Open();
                   CheckUserInFo();
                   Console.WriteLine("打开成功");
                   Console.WriteLine(strMsg);
               }
               catch (Exception ex)
               {
                   Console.WriteLine("异常:{0}", ex.Message);
               }
               finally
               {
                   //关闭数据
                   con.Close();
                   Console.WriteLine("关闭成功");
                   Console.ReadLine();                 
               }
           } 
           #endregion

        #region
           public string CheckUserInFo() 
           {
               
               Console.Write("请输入QQ号:");
               int ID = int.Parse(Console.ReadLine());
               Console.Write("请输入密码:");
               string pwd = Console.ReadLine();
               string sql =string.Format("select QQid,password from qquser where qqid={0} and password={1}",ID,pwd);
               SqlCommand com = new SqlCommand(sql,con);
               int i = (int)com.ExecuteScalar();
               if (i != 1)
               {
                   strMsg = "输入错误";
                   return strMsg;
               }
               else
               {
                   strMsg = "登陆成功";
                   return strMsg;
               }
           }

        #endregion
    }
}