This blog defines how to close a Window Form.
//closing button
private void close_btn_Click(object sender, EventArgs e)
{
DialogResult dialog = MessageBox.Show("do u want to close", "Exit", MessageBoxButtons.YesNo);
if (dialog == DialogResult.Yes)
{
Application.Exit();
}
else if (dialog == DialogResult.No)
{
// e.Cancel = true;
}
}