private void buttonStart_Click(object sender, EventArgs e) { string firstOperand = firstBox.Text; string secondOperand = secondBox.Text; if (Int32.Parse(firstOperand) >= Int32.Parse(secondOperand)) { try { var newSum = new SumAlgorithm(); newSum.calculateSum(Int32.Parse(firstOperand), Int32.Parse(secondOperand)); } catch { MessageBox.Show("Invalid input."); } } else { MessageBox.Show("Invalid input."); } }