哪位大侠 帮我 分析下

在C#中登陆按钮代码private void button1_Click(object sender, System.EventArgs e)
  {
   switch(comboBox1.SelectedIndex)
   {
    case 0:
     if(textBox1.Text==""||textBox2.Text=="")
     {
      MessageBox.Show("用户名和密码不能为空","提示",MessageBoxButtons.RetryCancel,MessageBoxIcon.Information);
      return;
     }
     else
     {
      try
      {
       OleDbConnection conn=db.createdb();
       conn.Open();
       OleDbCommand cmd=new OleDbCommand("select count(*) from user_info where user_id='"+textBox1.Text+"'and user_pwd='"+textBox2.Text+"'and beizhu='1'",conn);
       int count=Convert.ToInt32(cmd.ExecuteScalar().ToString());
       if(count>0)
       {
        Form2 form=new Form2();
        form.Show();
        this.Hide();       }
      }
      catch(Exception ex)
      {
       MessageBox.Show("错误"+ex.ToString(),"错误");
      }
      
     }
     break;
default:
break;   }登陆：
public class Users
{
   private string username="";
   private string password="";
   public string UserName
   {
      get{return this.username;}
      set{this.username=value;}
   }
   public string Password
   {
      get{return this.password;}
      set{this.password=value;}
   }
   public string CheckUser()
   {
      SqlConnection con=new SqlConnection(ConfigurationSettings.AppSettings["ConStr"]);
      SqlCommand cmd=new SqlCommand();
      cmd.Connection=con;
      cmd.CommandText="select UserName,Password from Users where UserName=@uname";
      cmd.Parameters.Add("@uname",SqlDbType.VarChar,10);
      cmd.Parameters[0].Value=UserName;
      string pass="";
      try
      {
         con.Open();
         SqlDataReader reader=cmd.ExecuteReader();
         if(reader.Read())
         {
             pass=reader[1].ToString();
         }
         else
         {
             reader.Close();
             con.Close();
             return UserName+"用户存在！";
          }
          reader.Close();
          con.Close();