Task

In this task, you will get a DateTime object based on the user input. After that, you will calculate the next and previous days (see Figure 11-1).

Figure 11-1 Calculating the next and previous days

Solution

The point is to use the Convert. ToDateTime method. If the user enters a nonexistent day (February 29 of a nonleap year, for example), the method causes a runtime error that you can deal with using the try-catch construction.

static void Main(string[] args)
{
    try
    {
        // Text input of date
        Console.Write("Enter date: ");
        string input = Console.ReadLine();

        // Conversion to DateTime object
        DateTime enteredDate = Convert.ToDateTime(input);

        // Some calculations
        DateTime followingDay = enteredDate.AddDays(1);
        DateTime previousDay  = enteredDate.AddDays(-1);

        // Outputs
        Console.WriteLine();
        Console.WriteLine("Entered day  : " + enteredDate.ToLongDateString());
        Console.WriteLine("Following day: " + followingDay.ToLongDateString());
        Console.WriteLine("Previous day : " + previousDay.ToLongDateString());
    }
    catch (Exception)
    {
        // Treating incorrect input
        Console.WriteLine("Incorrect input");
    }

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

Discussion

You can also call the Convert.ToDateTime method with two parameters instead of one. The second parameter is the language setting, which is the CultureInfo object you already know. This is similar to other conversion methods.

Task

A user enters a date. This program displays the first and last days of the month in which the entered date falls (see Figure 11-2).

Figure 11-2 Calcuating the first and last days of the month

Solution

Here is the code:

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

    // Calculations
    int enteredYear = enteredDate.Year;
    int enteredMonth = enteredDate.Month;

    DateTime firstDayOfMonth = new DateTime(enteredYear, enteredMonth, 1);
    DateTime lastDayOfMonth = firstDayOfMonth.AddMonths(1).AddDays(-1);

    // Outputs
    Console.WriteLine();
    Console.WriteLine("Corresponding month: " +
        "from " + firstDayOfMonth.ToShortDateString() +
        " to " + lastDayOfMonth.ToShortDateString());

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

Discussion

Note the following:

• According to the previous exercise, you get a DateTime object from the user using the Convert.ToDateTime method call.

• You start picking the month and year numbers from the entered date. You use the Month and Year properties for that purpose.

• Using these numbers, you easily assemble the first day of the month because its day number is always 1.

• The last day of the month is not that easy because months differ in length. The trick is to add a month and subtract a day!

• Note that I do not store AddMonth’s result anywhere. I directly call AddDays upon it instead. This is called method chaining.

• For the sake of simplicity, I do not deal with the possibility of incorrect input here.

Task

For the entered day, this program will display the beginning, end, and number (from 1 to 4) of the year’s quarter that the day belongs to (see Figure 11-3 and Figure 11-4).

Figure 11-3 Showing the corresponding quarter

Figure 11-4 Showing the corresponding quarter, another example

Analysis

The key to this task is to determine the quarter’s number. From that, the quarter’s first month follows.

int numberOfQuarter = (enteredMonth + 2) / 3;

int monthOfQuarterStart = 3 * numberOfQuarter - 2;

Solution

Here is the code:

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

    // Calculations
    int enteredYear = enteredDate.Year;
    int enteredMonth = enteredDate.Month;

    int numberOfQuarter = (enteredMonth + 2) / 3;
    int monthOfQuarterStart = 3 * numberOfQuarter - 2;
    DateTime firstDayOfQuarter = new DateTime(enteredYear, monthOfQuarterStart, 1);
    DateTime lastDayOfQuarter = firstDayOfQuarter.AddMonths(3).AddDays(-1);

    // Outputs
    Console.WriteLine();
    Console.WriteLine("Corresponding quarter: " +
        "number-" + numberOfQuarter +
        ", from " + firstDayOfQuarter.ToShortDateString() +
        " to " + lastDayOfQuarter.ToShortDateString());

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

Task

A user enters the date of her birth. The program displays how many days the world is happy to have her (see Figure 11-5).

Figure 11-5 Calculating how many days alive

Solution

As you can see, you need to subtract the birth date from today’s date. When you subtract dates, the result is a TimeSpan object. With this object in hand, you can use one of its many properties. You will use the Days property in this exercise.

Here is the code:

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

    // Today
    DateTime today = DateTime.Today;

    // Date difference
    TimeSpan difference = today - dateOfBirth;
    int numberOfDays = difference.Days;

    // Output
    Console.WriteLine();
    Console.WriteLine("Today is: " + today.ToShortDateString());
    Console.WriteLine("The world likes you for this number of days: " + numberOfDays.ToString("N0"));

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

Task

In this exercise, I will show you how to work both with UTC and with the time zones included in a DateTimeOffset object. You will make a program that works with the current time (see Figure 11-6).

Figure 11-6 DateTimeOffset object

Solution

Here is the code:

static void Main(string[] args)
{
    // Current time serves as input
    DateTime now = DateTime.Now;
    DateTime utcNow = DateTime.UtcNow;
    DateTimeOffset completeInstant = DateTimeOffset.Now;
    DateTimeOffset utcCompleteInstant = DateTimeOffset.UtcNow;

    // Outputs
    Console.WriteLine("Now: " + now);
    Console.WriteLine("UTC now: " + utcNow);
    Console.WriteLine("Now (including time zone): " + completeInstant);
    Console.WriteLine("Time zone (offset against UTC): " + completeInstant.Offset.TotalHours);
    Console.WriteLine("UTC now (including time zone): " + utcCompleteInstant);

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

Please note that some variables are of the DateTime type, while others are of the DateTimeOffset type.