how to compare value from table with textbox value

Hi,
 Try this Code :
SqlConnection con = new SqlConnection("Data Source=.\\SQLEXPRESS;Initial Catalog=DBNAME;Integrated Security=true;");

SqlDataReader dr;
SqlCommand cmd;

try
{
  con.Open();
  string qry ="select * from table where username ='"+textbox1.Text+"'";
  cmd = SqlCommand(qry,con);
  dr = cmd.ExecuteReader();
 while(dr.read())
  {
    //do something
    MessageBox.Show("UserName:"+dr.GetString(0));
  }
  dr.Close();
  con.Close();
}
catch(Exception ex)
{
  MessageBox.Show(ex.message);
}
finally
{
con.Close();
}