Task

After accepting an amount in euros and the euro exchange rate, you will convert the amount to dollars (see Figure 10-1).

Figure 10-1 Converting to dollars

Solution

Here is the code:

static void Main(string[] args)
{
    // Inputs
    Console.Write("Enter amount in euros: ");
    string inputEuros = Console.ReadLine();
    double amountEuros = Convert.ToDouble(inputEuros);

    Console.Write("Enter euro exchange rate (how many dollars per 1 euro): ");
    string inputExchangeRate = Console.ReadLine();
    double euroEchangeRate = Convert.ToDouble(inputExchangeRate);

    // Calculation
    double amountDollars = amountEuros * euroEchangeRate;

    // Output
    Console.WriteLine();
    Console.WriteLine("Amount in dollars: " + amountDollars);

    // Waiting for Enter
    Console.ReadLine();
}

Task

Say one of your customers buys several items, some of them possibly multiple times. You need to calculate the total price including the shipping cost. In this program, the prices and amounts of two products, as well as the shipping price, will be fixed directly in the source code for simplicity (see Figure 10-2).

Figure 10-2 Calculating total costs

Solution

Here is the code:

static void Main(string[] args)
{
    // Fixed values
    const double bookPrice = 29.8;
    const double dvdPrice = 9.9;
    const double shipmentPrice = 25;

    // Inputs
    Console.WriteLine("Order");
    Console.WriteLine("-----");

    Console.Write("Product "C# Programming for Absolute Beginners (book)" - enter number of pieces: ");
    string inputBookPieces = Console.ReadLine();
    int bookPieces = Convert.ToInt32(inputBookPieces);

    Console.Write("Product "All Quiet on Western Front (DVD)" - enter number of pieces: ");
    string inputDvdPieces = Console.ReadLine();
    int dvdPieces = Convert.ToInt32(inputDvdPieces);

    // Calculations
    double totalForBook = bookPrice * bookPieces;
    double totalForDvd = dvdPrice * dvdPieces;
    double totalForOrder = totalForBook + totalForDvd + shipmentPrice;

    // Outputs
    Console.WriteLine();
    Console.WriteLine("Order calculation");
    Console.WriteLine("-----------------");
    Console.WriteLine("Book: " + totalForBook);
    Console.WriteLine("Dvd: " + totalForDvd);
    Console.WriteLine("Shipment: " + shipmentPrice);
    Console.WriteLine("TOTAL: " + totalForOrder);

    // Waiting for Enter
    Console.ReadLine();
}

Discussion

Prepending fixed “variables” with const says they are constants, which are values that are not going to change in the course of the program run. Visual Studio does not allow you to assign new values to these “variables.”

Personally, I do not use const often. I just wanted to show it to you in case you see it during the course of your work.

Task

You will write a program that accepts the price of a product and then calculates the percentage of commission for the merchant, distributor, and producer. From the data, it also calculates the income division among the three parties (see Figure 10-3).

Figure 10-3 Calculating commissions

Solution

Here is the code:

static void Main(string[] args)
{
    // Inputs
    Console.Write("Enter customer price of product: ");
    string inputPrice = Console.ReadLine();
    double customerPrice = Convert.ToDouble(inputPrice);

    Console.Write("Enter merchant commission (percents): ");
    string inputMerchantPercents = Console.ReadLine();
    int merchantPercents = Convert.ToInt32(inputMerchantPercents);

    Console.Write("Enter distributor commission (percents): ");
    string inputDistributorPercents = Console.ReadLine();
    int distributorPercents = Convert.ToInt32(inputDistributorPercents);

    // Calculations
    double coeficient1 = 1 - merchantPercents / 100.0;
    double coeficient2 = 1 - distributorPercents / 100.0;

    double wholesalePrice = customerPrice * coeficient1;
    double priceAfterCommissionSubtraction = wholesalePrice * coeficient2;

    double merchantIncome = customerPrice - wholesalePrice;
    double distributorIncome = wholesalePrice - priceAfterCommissionSubtraction;
    double producerIncome = priceAfterCommissionSubtraction;

    // Outputs
    Console.WriteLine();
    Console.WriteLine("Income division");
    Console.WriteLine("----------------");
    Console.WriteLine("Merchant: " + merchantIncome);
    Console.WriteLine("Distributor: " + distributorIncome);
    Console.WriteLine("Producer: " + producerIncome);

    // Waiting for Enter
    Console.ReadLine();
}

Discussion

Sometimes commission percentages might be decimal numbers . I have chosen integers in this example because I wanted to show you how to correctly divide integers with a practical example. As you know, to perform “normal” division, you need at least one number—either in front of or after a slash—to be a double. That is why you use 100.0.

If you used 100 instead, the result would be surprising (see Figure 10-4).

Figure 10-4 Commission percents, incorrect

Do you know why this happens? It’s all because of rounding.

Task

After the user enters two monetary amounts (possibly somehow calculated with more than two decimal places), the program will display them with percent precision, round them to cents, and finally compare the calculation with the original values to the one with rounded values (Figure 10-5).

Figure 10-5 Rounding program

Solution

Here is the code:

static void Main(string[] args)
{
    // For simplicity, inputs are fixed in program
    // Some amounts, e.g. after commission calculations, cent fractions are possible
    double amount1 = 1234.567;
    double amount2 = 9.876;

    // Displaying inputs (original values)
    Console.WriteLine("First amount (original value): " + amount1);
    Console.WriteLine("Second amount (original value): " + amount2);
    Console.WriteLine();

    // Rounding just for output
    Console.WriteLine("First amount displayed with cent precision: " + amount1.ToString("N2"));
    Console.WriteLine("Second amount displayed with cent precision: " + amount2.ToString("N2"));
    Console.WriteLine();

    // Rounding for further calculations + informative output
    double roundedAmount1 = Math.Round(amount1, 2); // 2 = two decimal places
    double roundedAmount2 = Math.Round(amount2, 2);

    Console.WriteLine("First amount rounded to cents: " + roundedAmount1);
    Console.WriteLine("Second amount rounded to cents: " + roundedAmount2);
    Console.WriteLine();

    // Calculations
    double sumOfOriginalAmounts = amount1 + amount2;
    double sumOfRoundedAmounts = roundedAmount1 + roundedAmount2;

    // Calculation outputs
    Console.WriteLine("Sum of original amounts: " + sumOfOriginalAmounts.ToString("N2"));
    Console.WriteLine("Sum of rounded amounts: " + sumOfRoundedAmounts.ToString("N2"));
    Console.WriteLine("On invoice, we need sum of rounded amounts");

    // Waiting for Enter
    Console.ReadLine();
}

Task

In this task, I will show you how to round to dollars, round to hundreds of dollars, always round down, and always round up (see Figure 10-6 and Figure 10-7).

Figure 10-6 More complicated rounding

Figure 10-7 Another number to round to dollars, cents, and hundreds of dollars

Solution

Here is the code:

static void Main(string[] args)
{
    // Input
    Console.Write("Enter (decimal) amount in dollars: ");
    string input = Console.ReadLine();
    double amount = Convert.ToDouble(input);

    // To dollars
    double nearest    = Math.Round(amount);
    double alwaysDown = Math.Floor(amount);
    double alwaysUp   = Math.Ceiling(amount);

    Console.WriteLine();
    Console.WriteLine("To dollars");
    Console.WriteLine("----------");
    Console.WriteLine("Nearest    : " + nearest);
    Console.WriteLine("Always down: " + alwaysDown);
    Console.WriteLine("Always up  : " + alwaysUp);

    // To cents
    nearest    = Math.Round(amount, 2);
    alwaysDown = Math.Floor(100 * amount) / 100;
    alwaysUp   = Math.Ceiling(100 * amount) / 100;

    Console.WriteLine();
    Console.WriteLine("To cents");
    Console.WriteLine("--------");
    Console.WriteLine("Nearest    : " + nearest);
    Console.WriteLine("Always down: " + alwaysDown);
    Console.WriteLine("Always up  : " + alwaysUp);

    // To hundreds of dollars
    nearest    = 100 * Math.Round(amount / 100);
    alwaysDown = 100 * Math.Floor(amount / 100);
    alwaysUp   = 100 * Math.Ceiling(amount / 100);

    Console.WriteLine();
    Console.WriteLine("To hundreds of dollars");
    Console.WriteLine("----------------------");
    Console.WriteLine("Nearest    : " + nearest);
    Console.WriteLine("Always down: " + alwaysDown);
    Console.WriteLine("Always up  : " + alwaysUp);

    // Waiting for Enter
    Console.ReadLine();
}

Task

In this task, you will create a simple VAT calculator (see Figure 10-8). The program starts from the price a customer pays for a product and calculates the price without VAT (the merchant gets from the purchase) and also the VAT itself (what the merchant transfers to the tax administrator).

Figure 10-8 Calculating VAT

Analysis

If you want to program something, you have to understand the essence of that something first. So, how does the European VAT work?

The foundation of the calculation is the price without VAT. To get this price, the appropriate percent part (for example, 21 percent) is added, and you get the price a customer pays. What is important is that the percents are calculated from the price without VAT, not from the customer price (see Figure 10-9)!

Figure 10-9 Understanding how the VAT works

If the VAT rate is, for example, 21 percent, you need to divide the customer price by 1.21 to get the price without the VAT. For the general value of the tax rate, you calculate the divisor by adding the appropriate fraction to 1.

Solution

Here is the code:

static void Main(string[] args)
{
    // Inputs
    Console.Write("Enter customer price of a product: ");
    string inputPrice = Console.ReadLine();
    double customerPrice = Convert.ToDouble(inputPrice);

    Console.Write("Enter VAT rate in %: ");
    string inputVatRate = Console.ReadLine();
    double vatRate = Convert.ToDouble(inputVatRate);

    // Calculations
    double divisor = 1 + vatRate / 100.0;
    double calculatedPriceWithoutVat = customerPrice / divisor;
    double priceWithoutVat = Math.Round(calculatedPriceWithoutVat, 2);
    double vat = customerPrice - priceWithoutVat;

    // Outputs
    Console.WriteLine();
    Console.WriteLine("Price without VAT: " + priceWithoutVat.ToString("N2"));
    Console.WriteLine("VAT: " + vat.ToString("N2"));

    // Waiting for Enter
    Console.ReadLine();
}