private void Change_Click(object sender, EventArgs e) { if (textBoxAmountCh.Text != "" || textBoxCurrencyFrom.Text != "" || textBoxCurrencyTo.Text != "") { result.Text = Changer.change(Convert.ToDouble(textBoxAmountCh.Text), Changer.choose(textBoxCurrencyFrom.Text), Changer.choose(textBoxCurrencyTo.Text)).ToString(); result.Visible = true; } else { MessageBox.Show("Try to fill all fields correctly"); } }