private void button1_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < dataGridView1.Rows.Count; i++)
            {

                DataGridViewCheckBoxCell chk = (DataGridViewCheckBoxCell)dataGridView1.Rows[i].Cells[0];
                if ((Boolean)chk.EditedFormattedValue == true)
                {

                    string username = dataGridView1.Rows[i].Cells["username"].Value.ToString();
                    string userid = dataGridView1.Rows[i].Cells["userid"].Value.ToString();
}

            }