C＃中的数学错误

Question

I am currently writing the code for a Shop program in C#. I am relatively new to C# and I am having difficulty in getting the math to work in the following piece of code:

//Add Basket
public void addBasket()
{
   //Add up the total of individual items
   double total = 0;
   if (shoppingCart.Count() == 0)
   {
      Console.WriteLine("ERROR - Basket is Empty");
   }
   else
   {
      foreach (Products tmp in shoppingCart)
      {
         total = (tmp.Price * tmp.BoughtStock);
         Console.WriteLine("The cost of the individual item  is: " + "\t" +total);
      }
   }
   //Calculate the products together
   double itemTotal = 0;
   if (shoppingCart.Count() == 0)
   {
      Console.WriteLine("ERROR - Basket is Empty");
   }
   else
   {
      foreach (Products tmp in shoppingCart)
      {
         itemTotal = (tmp.Price * tmp.BoughtStock);
         itemTotal = itemTotal + total;
         Console.WriteLine("The cost of the items together is: \t" +itemTotal);
      }
      //Calculate VAT 
      double vatPrice = total * .21;
      double netPriceBeforeDiscount = total + vatPrice;

      //calculate discount: if total cost of shop is over 25 give 10% discount.
      if (netPriceBeforeDiscount >= 25)
      {
         double reducedPrice = netPriceBeforeDiscount * .10;
         double netPrice = netPriceBeforeDiscount - reducedPrice;
         reducedPrice = Math.Round(reducedPrice, 2);
         netPrice = Math.Round(netPrice, 2);

         Console.WriteLine("Discount*:\t\t\t\t " + reducedPrice);
         Console.WriteLine("\nTotal Net Cost (including VAT and discounts):\t      Euro " + netPrice);
      }
      else
      {
         double netPrice = Math.Round(netPriceBeforeDiscount, 2);
      }
   }
}

The first part of the code works correctly, as in that it adds any products in the basket and displays there prices individually, the problem arises in the second part, adding the items in the baskets prices together. As you can see in the output http://gyazo.com/1656eecc689b7a9d0bfc47b8480169a6 (I have to link a screencap of the output as I don't know how to show output from C# on here) It displays the total of the first item, the second item and then correctly adds them two results together, although I don't know why it displays the cost of the second item multiplied by two. Finally as you may see at the bottom of the code, I have written what i believe to be a correct way of getting the VAT and displaying a bulk discount but from the link above when I use two items the code will not calculate or display the VAT or bulk discount yet with one item in the basket it will, see here > ( * Link Number 1 Below goes here *) . Again though ,from what I imagine is the error causing the other parts of the code to not work properly, when I do just one item despite calculating the vat and bulk discounts correctly and displaying the correct answer it multiplys the individual item cost by the amount of the product I bought, see here > ( * Link Number 2 Below goes here *)

As I said though I am new to this and well not exactly great at C# but any help would be greatly appreciated and if you require anything from me just ask, Thanks

Edit* : Just realised I need 10 reputation to post more than two links, I link the 2 missing links in the comments below.

Answer 1

foreach (Products tmp in shoppingCart)
        {
            total = (tmp.Price * tmp.BoughtStock);

You probably mean for it to be total += , otherwise you are only keeping the last value.

Answer 2

Your second loop:

        foreach (Products tmp in shoppingCart)
        {
            itemTotal = (tmp.Price * tmp.BoughtStock);
            itemTotal = itemTotal + total;
            Console.WriteLine("The cost of the items together is: \t" +itemTotal);
        }

Is also very odd. You are again overwriting itemTotal each time round the loop, but then just adding the previously calculated total to this result.

I don't know what you are intending here so I hesitate to suggest that you just need to use += again - but it's definitely wrong.

However your Console.WriteLine statement appear to suggest that you want to display the price of each line in the transaction. In that case you'll need to do something like this:

decimal transactionTotal = 0;
foreach (Products tmp in shoppingCart)
{
    decimal lineTotal = (tmp.Price * tmp.BoughtStock);
    transactionTotal += lineTotal;
    Console.WriteLine("The cost of the items together is: \t" + lineTotal);
}

Note that I'm using decimal as this gives more consistent results when dealing with money.