using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Data.SqlClient;

namespace WindowsFormsApplication1.App_Code

{

    public class UsersData

    {

        SqlConnection conn = null;

        SqlCommand cmd = null;

        public UsersData()

        {

            conn = new SqlConnection("server=.;database=Data0216;user=sa;pwd=123");

            cmd = conn.CreateCommand();

        }

        //查询是否存在该帐号

        public bool SelectHasName(string name)

        {

            bool has = false;

            cmd.CommandText = "select * from Users where UserName=@a";

            cmd.Parameters.Clear();

            cmd.Parameters.AddWithValue("@a",name);

            conn.Open();

            SqlDataReader dr = cmd.ExecuteReader();

            if (dr.HasRows)

            {

                has = true;

            }

            conn.Close();

            return has;

        }

    //如果存在，查询该用户下对应的密码

        public string SelectPassWord(string name)

        {

            string end="";

            cmd.CommandText = "select PassWord from Users where UserName=@a";

            cmd.Parameters.Clear();

            cmd.Parameters.AddWithValue("@a",name);

            conn.Open();

            SqlDataReader dr = cmd.ExecuteReader();

            dr.Read();

            end = dr["PassWord"].ToString();

            conn.Close();

            return end;

        }

    }

}

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

using WindowsFormsApplication1.App_Code;

namespace WindowsFormsApplication1

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void Form1_Load(object sender, EventArgs e)

        {

        }

        private void button1_Click(object sender, EventArgs e)

        {

            string username = textBox1.Text;

            string password = textBox2.Text;

            UsersData ud = new UsersData();

            bool HasName = ud.SelectHasName(username);

            //如果帐号存在

            if (HasName)

            {

                //查询该帐号对应的密码是否与用户输入的一致

                if (password == ud.SelectPassWord(username))

                {

                    MessageBox.Show("帐号密码匹配成功！");

                }

                else MessageBox.Show("您输入的密码不正确！");

            }

            else MessageBox.Show("您输入的账户不存在！");

        }

    }

}