private void BtnEquals_Click(object sender, RoutedEventArgs e) { double newNumber; if (double.TryParse(lblResult.Content.ToString(), out newNumber)) { switch (selectedOperator) { case SelectedOperator.Addition: result = SimpleMath.Add(lastNumber, newNumber); break; case SelectedOperator.Subtraction: result = SimpleMath.Minus(lastNumber, newNumber); break; case SelectedOperator.Multiplication: result = SimpleMath.Times(lastNumber, newNumber); break; case SelectedOperator.Division: result = SimpleMath.Divide(lastNumber, newNumber); break; } } lblResult.Content = result.ToString(); }