Question

I experimented a lot with re throwing exceptions and came on to following conclusions:

1)We might want to re throw if we want to give more details about exception like (Inner exception)

2)we may re throw to entirely terminate the program ..

3)if we want to re throw and do not want to terminate the program then i will have to handle the re thrown exception in a loop …

i tried the following while doing this:

 public void input()
        {
            char opt;
            int id;
            int qty;
            int ind = -1;

            do
            {
                Console.WriteLine("Add item to  cart:   ");
                opt = Convert.ToChar(Console.ReadLine());
                if (opt == 'n' || opt == 'N')
                    break;
                else
                {
                    cashier.showProductList();
                    Console.WriteLine("Enter Product ID from above list:    ");
                    id = Convert.ToInt32(Console.ReadLine());
                    foreach (Products item in cashier.ProductList)
                    {
                        if (id == item.ProductID)
                        {
                            BoughtItems.Add(item);
                            ind = Cashier.ProductList.IndexOf(item);                        
                        }
                    }

                    Console.WriteLine("Enter The quantity required:     ");
                    qty = Convert.ToInt32(Console.ReadLine());
                    try
                    {
                        if (qty < 0)
                        {
                            throw new BuisnessException("Qty can not be -ve...", new Exception("enter a valid +ve amount"));
                        }
                        else if (qty < cashier.ProductList[ind].Quantity)
                        {
                            BoughtItems[BoughtItems.Count - 1].Quantity = qty;
                            TotalPrice = TotalPrice + (BoughtItems[BoughtItems.Count - 1].Quantity * BoughtItems[BoughtItems.Count - 1].price);
                        }
                        else if (qty >= cashier.ProductList[ind].Quantity)
                        {
                            throw new QuantityExceedingStockException("Item not in sufficient amount", new Exception("Enter quantity less than" + Cashier.ProductList[ind].Quantity));
                        }
                    }
                    catch (BuisnessException ex)
                    {

                        BoughtItems.RemoveAt(BoughtItems.Count - 1);
                        Console.WriteLine(ex.Message);
                        throw;
                        //throw; //Re throwing terminating the i/p loop if re thrown exception not handled in loop! :/
                    }
                    catch (QuantityExceedingStockException ex)
                    {
                        BoughtItems.RemoveAt(BoughtItems.Count - 1);
                        Console.WriteLine(ex.Message);
                        throw;
                    }
                }

            } while (true);
        }

        public void showCartItems()
        {
            foreach (Products item in _boughtItems)
            {
                Console.WriteLine(item.ProductID + "  " + item.name + "  " + item.price + "  " + item.Quantity);
            }
        }

then in main():

            do
        {
            try
            {
                cashier1.Customr.input();
            }
            catch (BuisnessException ex)
            {
                //Console.WriteLine(ex.Message);
                Console.WriteLine(ex.InnerException.Message);
            }
            catch (QuantityExceedingStockException ex)
            {
                Console.WriteLine(ex.InnerException.Message);
            }
            //catch
            //{
            //    Console.WriteLine("Press y below to continue shopping");
            //}
            Console.Write("Continue Shopping ?");
            opt = Convert.ToChar(Console.ReadLine());
            if (opt == 'n')
                break;
            else
                continue;
        } while (true);
        Console.WriteLine("Total Price is:  " + cashier1.Customr.TotalPrice);

If i do not handle the re thrown exception in loop my program terminates … So does this means that above three Conclusions tat i presented are correct regarding re throwing exceptions??

Answer 1

Your conclusions are correct. I am assuming that in conclusion 1 you mean that rethrowing an exception gives you a chance to log an error.

But your approach is unconventional. Normally exceptions are not used to handle business logic cases. Why not modify your loop like this (replace you “try/catch” block)?

if (qty < 0)
{
    BoughtItems.RemoveAt(BoughtItems.Count - 1);
    // The code below has been EDITED to show throwing an exception in the same block
    // as the related logic.
    string message = "Qty can not be -ve, enter a valid +ve amount"; // EDITED
    Console.WriteLine(message);
    throw new BusinessException(message); // EDITED
}
else if (qty < cashier.ProductList[ind].Quantity)
{
    BoughtItems[BoughtItems.Count - 1].Quantity = qty;
TotalPrice = TotalPrice + (BoughtItems[BoughtItems.Count - 1].Quantity * BoughtItems[BoughtItems.Count - 1].price);
}
else if (qty >= cashier.ProductList[ind].Quantity)
{
    BoughtItems.RemoveAt(BoughtItems.Count - 1);
    Console.WriteLine("Item not in sufficient amount, enter quantity less than " + Cashier.ProductList[ind].Quantity);
}