string ConnectionString = @"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\matri\Desktop\test\DatabaseProject\DatabaseProject\database.mdf;Integrated Security = True";

using (SqlConnection con = new SqlConnection(ConnectionString))
{
	con.Open();
	using (SqlCommand cmd = new SqlCommand("SELECT * FROM Users", con))
	{
		SqlDataReader reader = cmd.ExecuteReader();
		while (reader.Read())
		{
			MessageBox.Show("username = " + reader["username"].ToString() + " & password =" + reader["password"].ToString());
		}
		reader.Close();

		cmd.ExecuteNonQuery();
	}
}