C#怎么实现用户登录?

追问：??请详细说明下？

答案：登录涉及到检索数据的处理，详细如下：
登录界面：
后台代码：
            SqlConnection conn = new SqlConnection("server=服务器;database=数据库;user id=数据库用户名;password=密码");
            string Str = String.Format("select StuName,Pwd from StuNo where StuName='{0}'", UserId.Text.Trim());
            SqlCommand comm = new SqlCommand(Str, conn);     
   try
        {
           
             conn.Open();
            SqlDataReader dr = comm.ExecuteReader();
            if (dr.Read())
            {
               
                if (dr["Pwd"].ToString().Trim() == UserPwd.Text.Trim())
                {
                    Response.Write("登录成功！");
                }
                else
                {
                    Response.Write("<script language=javascript > alert('密码错误！')</script>");
                }
            }
            else
            {
                Response.Write("<script language=javascript > alert('用户名不存在或错误！')</script>");
            }
        }
        catch (Exception ee)
        {
            Response.Write(ee.Message);
        }
        finally
        { conn.Close(); }

    }
登录功能存在很有趣的逻辑，你可以仔细琢磨琢磨。
这是我的一个登录部分的代码：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace QQ
{
    public partial class LoginForm : Form
    {
        public LoginForm()
        {
            InitializeComponent();
        }

        private void label1_Click(object sender, EventArgs e)
        {
            this.Hide();
            RegisterForm2 rg2 = new RegisterForm2();
            rg2.Show();
        }

        private void cboId_Click(object sender, EventArgs e)
        {
            if (cboId.Text.Trim() == "<请输入帐号>")
            {
                cboId.Text = "";
            }
        }
        private void cboId_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (!(e.KeyChar >= '0' && e.KeyChar <= '9') && (int)e.KeyChar != 8)
            {
                e.Handled = true;
            }
        }
        private void 我在线上ToolStripMenuItem1_Click(object sender, EventArgs e)
        {
            toolStripStatusLabel1.Image=imageList1.Images[0];
            UserHelp.state = "我在线上";
        }
        private void q我吧ToolStripMenuItem1_Click(object sender, EventArgs e)
        {
             toolStripStatusLabel1.Image=imageList1.Images[3];
             UserHelp.state = "Q我吧";
        }
        private void 离开ToolStripMenuItem1_Click(object sender, EventArgs e)
        {
             toolStripStatusLabel1.Image=imageList1.Images[4];
             UserHelp.state = "离开";
         }
        private void 忙碌ToolStripMenuItem1_Click(object sender, EventArgs e)
        {
             toolStripStatusLabel1.Image=imageList1.Images[2];
             UserHelp.state = "忙碌";
        }
        private void 请勿打扰ToolStripMenuItem1_Click(object sender, EventArgs e)
        {
             toolStripStatusLabel1.Image=imageList1.Images[5];
             UserHelp.state = "请勿打扰";
        }
        private void 隐身ToolStripMenuItem_Click(object sender, EventArgs e)
        {
        

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