private void Hole_Leave(object sender, EventArgs e) { DialogResult re; if (long.TryParse(Hole.Text, out long mynum)) { if (mynum < 0) { re = MessageBox.Show("Error"); if (re == DialogResult.OK) { Hole.Clear(); } return; } number = mynum; } else { re = MessageBox.Show("Error"); if (re == DialogResult.OK) { Hole.Clear(); } } }