登录界面的修改密码，作业求帮助

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;
namespace 任务
{
public partial class Form3 : Form
{
public Form3()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
}
}
}
登录界面的修改密码，作业求帮助

一份作业，开学要交，拖好按钮什么的就闷逼了。完全不会写啊。有没有高手给个完整版的。要有和数据库互动的。

解决方案

  public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
        }
        private void button1_Click(object sender, EventArgs e)
        {
            if (textBox1.Text.Trim().Length == 0 )
            {
                MessageBox.Show("用户名不能为空！");
                return;
            }
            else if (textBox2.Text.Trim().Length == 0)
            {
                MessageBox.Show("原密码不能为空！");
                return;
            }
            else if(textBox3.Text.Trim().Length == 0)
            {
                MessageBox.Show("新密码不能为空！");
                return;
            }
            String ConnString = "Server=.;Database=User;Integrated Security=SSPI";
            SqlConnection conn = new SqlConnection(ConnString);
            DataTable dt = new DataTable();
            String sql = "SELECT USERNAME,PASSWORD FROM USERINFO where USERNAME= "" + textBox1.Text + "" and PASSWORD = "" + textBox2.Text.Trim()+""";
            try
            {
                SqlDataAdapter da = new SqlDataAdapter(sql, conn);
                da.Fill(dt);
            }
            catch (Exception Err)
            {
                MessageBox.Show(Err.Message);
            }
            if (dt.Rows.Count == 0)
            {
                MessageBox.Show("旧密码输入错误！");
                dt.Dispose();
            }
            else
            {
                sql = "UPDATE USERINFO set PASSWORD ="" + textBox3.Text.Trim() + "" where USERNAME= "" + textBox1.Text + """;
                SqlCommand cmd = new SqlCommand();
                cmd.CommandText = sql;
                cmd.Connection = conn;
                try
                {
                    conn.Open();
                    cmd.ExecuteNonQuery();
                }
                catch (Exception Err)
                {
                    MessageBox.Show("更新出现异常！");
                }
                finally
                {
                    conn.Close();
                }
                MessageBox.Show("密码更新成功！");
            }
        }

要项目不？