Task

You will write a program that appends the .png extension to the entered file name unless the extension is already part of the input (see Figures 16-1 and 16-2).

Figure 16-1 Appending the .png extension

Figure 16-2 Not appending the .png extension

Solution

Here is the code:

static void Main(string[] args)
{
    // Input
    Console.Write("Enter image name: ");
    string fileName = Console.ReadLine();

    // Appending extension (ONLY IN CASE OF NEED)
    if (!fileName.ToLower().EndsWith(".png"))
    {
        fileName += ".png";
    }

    // Output
    Console.WriteLine("We are going to use name: " + fileName);

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

Discussion

Let’s discuss this program a bit.

Task

You will write a program that throws a coin once (see Figure 16-3).

Figure 16-3 Throwing a coin

Solution

The core of the solution is to generate a random number—zero or one—and convert it to heads or tails subsequently.

Here is the code:

static void Main(string[] args)
{
    // Random number generator
    Random randomNumbers = new Random();

    // Random number 0/1 and its transformation
    int randomNumber = randomNumbers.Next(0, 1 + 1);
    if (randomNumber == 0)
    {
        Console.WriteLine("Head tossed");
    }
    else
    {
        Console.WriteLine("Tail tossed");
    }

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

Task

You will write a program that prompts the user to enter an order deadline and presents a warning if the user enters a date in the past (see Figure 16-4).

Figure 16-4 Checking a date

Solution

Here is the code:

static void Main(string[] args)
{
    // Input
    Console.Write("Enter order deadline: ");
    string input = Console.ReadLine();
    DateTime enteredDeadline = Convert.ToDateTime(input);

    // Checking entered value
    DateTime today = DateTime.Today;
    if (enteredDeadline < today)
    {
        Console.WriteLine("Error! You have entered date in the past.");
    }
    else
    {
        Console.WriteLine("Deadline accepted.");
    }

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

Task

Value-added tax (VAT) regulations in my country require that the date an invoice is issued cannot precede the date of payment, and at the same time, it cannot be later than 15 days after the payment.

The current task is to perform both checks (see Figure 16-5, Figure 16-6, and Figure 16-7).

Figure 16-5 Date too early

Figure 16-6 Date too late

Figure 16-7 Dates accepted

Solution

Here is the solution:

static void Main(string[] args)
{
    // Inputs
    Console.Write("Payment date: ");
    string inputPayment = Console.ReadLine();
    DateTime paymentDate = Convert.ToDateTime(inputPayment);

    Console.Write("Invoice date: ");
    string inputInvoice = Console.ReadLine();
    DateTime invoiceDate = Convert.ToDateTime(inputInvoice);

    // Checking
    bool ok = true;
    if (invoiceDate < paymentDate)
    {
        Console.WriteLine("Invoice date cannot precede payment date.");
        ok = false;
    }
    if (invoiceDate > paymentDate.AddDays(15))
    {
        Console.WriteLine("Invoice cannot be issued later than 15 days after payment.");
        ok = false;
    }
    if (ok)
    {
        Console.WriteLine("Dates accepted.");
    }

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

Task

You will write a program that displays the Spanish version of the day of week (lunes, martes, miércoles, and so on) for a date entered by the user (see Figure 16-8).

Figure 16-8 Displaying days in Spanish

Solution

You can find the day of the week using the DayOfWeek property of the DateTime object. The conversion to Spanish can be made using a series of conditions.

Here is the code:

static void Main(string[] args)
{
    // Input
    Console.Write("Enter a date: ");
    string input = Console.ReadLine();
    DateTime enteredDate = Convert.ToDateTime(input);

    // Finding day of week (in enumeration)
    DayOfWeek dayOfWeek = enteredDate.DayOfWeek;

    // Spanish texts
    string spanish = "";
    if (dayOfWeek == DayOfWeek.Monday)
        spanish = "Lunes";
    if (dayOfWeek == DayOfWeek.Tuesday)
        spanish = "Martes";
    if (dayOfWeek == DayOfWeek.Wednesday)
        spanish = "Miercoles";
    if (dayOfWeek == DayOfWeek.Thursday)
        spanish = "Jueves";
    if (dayOfWeek == DayOfWeek.Friday)
        spanish = "Viernes";
    if (dayOfWeek == DayOfWeek.Saturday)
        spanish = "Sábado";
    if (dayOfWeek == DayOfWeek.Sunday)
        spanish = "Domingo";

    // Output
    Console.WriteLine(spanish);
    if (enteredDate == new DateTime(1945, 5, 8))
        Console.WriteLine("The happiest day of the 20th century.");

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

Discussion

Note the following:

• You have omitted braces surrounding individual if branches. You can do that because there is only a single statement in every branch. I normally do not do this, but in this case of many simple ifs, it seemed to me that it would make the code neater.

• Individual days of the week are members of the DayOfWeek enumeration. Visual Studio offers you the enumeration as soon as you hit the spacebar on your keyboard after entering two equal signs (see Figure 16-9). Use what Visual Studio offers!

Figure 16-9 Using DayOfWeek enumeration

Task

You will solve the last task using a switch statement.

Solution

Here is the code:

static void Main(string[] args)
{
    // Input
    Console.Write("Enter a date: ");
    string input = Console.ReadLine();
    DateTime enteredDate = Convert.ToDateTime(input);

    // Finding day of week (in enumeration)
    DayOfWeek dayOfWeek = enteredDate.DayOfWeek;

    // Spanish texts
    string spanish = "";
    switch (dayOfWeek)
    {
        case DayOfWeek.Monday:
            spanish = "Lunes";
            break;
        case DayOfWeek.Tuesday:
            spanish = "Martes";
            break;
        case DayOfWeek.Wednesday:
            spanish = "Miercoles";
            break;
        case DayOfWeek.Thursday:
            spanish = "Jueves";
            break;
        case DayOfWeek.Friday:
            spanish = "Viernes";
            break;
        case DayOfWeek.Saturday:
            spanish = "Sábado";
            break;
        case DayOfWeek.Sunday:
            spanish = "Domingo";
            break;
    }

    // Output
    Console.WriteLine(spanish);
    if (enteredDate == new DateTime(1945, 5, 8))
        Console.WriteLine("The happiest day of the 20th century.");

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