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Understanding C# Types

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Other Commonly Used Types

In addition to the standard predefined types, the .NET Framework provides types for other commonly used values. These types do not have aliases in C# like the predefined types but allow the same operations.

Date and Time

Working with date and time values is done with the DateTime structure, which enables you to create values that represent a date and a time, just a date, or just a time value. The two most common ways to create a new DateTime value are to use one of the various constructor overloads or one of the four static parse methods: Parse, ParseExact, TryParse, or TryParseExact.

The DateTime structure provides several properties; the most common are shown in Table 3.2.

Table 3.2. Common DateTime Properties

Property

Description

Date

Gets the date component of the current instance

Day

Gets the day of the month represented by the current instance

DayOfWeek

Gets the day of the week represented by the current instance

Hour

Gets the hour component of the date represented by the current instance

Minute

Gets the minute component of the date represented by the current instance

Month

Gets the month component of the date represented by the current instance

Now

Gets a DateTime object that is set to the current date and time, in the local time zone

TimeOfDay

Gets the time of day for the current instance

Today

Gets the current date

UtcNow

Gets a DateTime object that is set to the current date and time, in Coordinated Universal Time (UTC)

Year

Gets the year component of the date represented by the current instance

When adding or subtracting date or time values, you can use instance methods, which return a new DateTime value rather than modifying the original one. The common DateTime arithmetic methods are shown in Table 3.3.

Table 3.3. Common DateTime Arithmetic Methods

Method

Description

AddDays

Adds or subtracts the specified number of days

AddHours

Adds or subtracts the specified number of hours

AddMinutes

Adds or subtracts the specified number of minutes

AddMonths

Adds or subtracts the specified number of months

AddYears

Adds or subtracts the specified number of years

It is also possible to subtract two DateTime values using the subtraction operator, which results in a TimeSpan instance. A TimeSpan represents an interval of time measured as a positive or negative number of days, hours, minutes, seconds, and fractions of a second. To ensure consistency, time intervals are measured in days. You can also add a TimeSpan to or subtract a TimeSpan from a DateTime, both of which result in a new DateTime value.

The common methods and properties of TimeSpan are shown in Table 3.4.

Table 3.4. Common TimeSpan Members

Name

Description

Add

Adds the specified TimeSpan to the current instance

Days

Gets the days component of the time interval represented by the current TimeSpan

FromDays

Returns a TimeSpan that represents a specified number of days

FromHours

Returns a TimeSpan that represents a specified number of hours

FromMilliseconds

Returns a TimeSpan that represents a specified number of milliseconds

FromMinutes

Returns a TimeSpan that represents a specified number of minutes

FromSeconds

Returns a TimeSpan that represents a specified number of seconds

Hours

Gets the hours component of the time interval represented by the current TimeSpan

Milliseconds

Gets the milliseconds component of the time interval represented by the current TimeSpan

Minutes

Gets the minutes component of the time interval represented by the current TimeSpan

Seconds

Gets the seconds component of the time interval represented by the current TimeSpan

Subtract

Subtracts the specified TimeSpan from the current instance

TotalDays

Gets the value of the current TimeSpan expressed as whole and fractional days

TotalHours

Gets the value of the current TimeSpan expressed as whole and fractional hours

TotalMilliseconds

Gets the value of the current TimeSpan expressed as whole and fractional milliseconds

TotalMinutes

Gets the value of the current TimeSpan expressed as whole and fractional minutes

TotalSeconds

Gets the value of the current TimeSpan expressed as whole and fractional seconds

Globally Unique Identifiers (GUIDs)

A GUID is a 128-bit integer value that can be used whenever a unique identifier is required that has a low probability of being duplicated. The System.Guid structure enables you to create and compare GUID values. The common members are shown in Table 3.5.

Table 3.5. Common Guid Members

Name

Description

CompareTo

Compares the current instance to the specified Guid

Empty

Represents a read-only instance of a Guid whose value is guaranteed to be all zeros

NewGuid

Creates a new instance of the Guid structure

Parse

Converts the string representation of a GUID into the equivalent Guid instance

TryParse

Converts the string representation of a GUID into the equivalent Guid instance, indicating if the conversion was successful

Uniform Resource Identifiers (URIs)

A uniform resource identifier (URI) is a compact representation of a resource available on the intranet or the Internet and can be an absolute URI (like a web page address) or a relative URI that must be expanded with respect to a base URI.

The Uri class enables you to create new URI values and access the parts of a URI, and provides methods for working with URIs, such as parsing, comparing, and combining. Some of the common members are shown in Table 3.6.

Table 3.6. Common Uri Members

Name

Description

AbsoluteUri

Gets the absolute URI

Compare

Compares the specified parts of two Uri instances using the specified comparison rules

EscapeUriString

Converts a URI string to its escaped representation

IsFile

Gets a value indicating whether the specified Uri is a file URI

LocalPath

Gets a local operating-system representation of a filename

MakeRelativeUri

Determines the difference between two Uri instances

TryCreate

Creates a new Uri but does not throw an exception if the Uri cannot be created

An instance of the Uri class is immutable. To create a modifiable URI, use the UriBuilder class. The UriBuilder class enables you to easily change the properties of a URI without creating a new instance for each modification. All the properties shown in Table 3.7 are common to both Uri (where they are read-only) and UriBuilder except for the Uri property, which is only available on UriBuilder.

Table 3.7. Common Uri and UriBuilder Properties

Name

Description

Fragment

Gets or sets the fragment portion of the URI

Host

Gets or sets the hostname or IP address of a server

Password

Gets or sets the password associated with the user who accesses the URI

Path

Gets or sets the path to the resource defined by the URI

Port

Gets or sets the port number of the URI

Query

Gets or sets any query information included in the URI

Scheme

Gets or sets the scheme name of the URI

Uri

Gets the Uri instance constructed by the specified UriBuilder instance

UserName

Gets or sets the username associated with the user who accesses the URI

Listing 3.1 shows how to use the UriBuilder class.

Listing 3.1. Working with UriBuilder

Uri immutableUri = new Uri("http://www.example.com");
Console.WriteLine(immutableUri);

UriBuilder mutableUri = new UriBuilder(immutableUri);
Console.WriteLine(mutableUri);

mutableUri.Scheme = "https";
mutableUri.Host = "www.example.com";
mutableUri.Path = "exampleFile.html";
Console.WriteLine(mutableUri);

Big Integers and Complex Numbers

The System.Numerics.BigInteger type represents an arbitrarily large integer value that has no theoretical upper or lower bound. When a BigInteger instance has been created, you can use it just as you would any of the other integer types, enabling you to perform basic mathematical operations and comparisons. Listing 3.2 shows some of the ways you can use the BigInteger type.

Listing 3.2. Working with BigInteger

BigInteger b1 = new BigInteger(987321.5401);
BigInteger b2 = (BigInteger)435623411897L;
BigInteger b3 = BigInteger.Parse("435623411897");

Console.WriteLine(BigInteger.Pow(Int32.MaxValue, 2));
Console.WriteLine(b2 == b3);
Console.WriteLine(BigInteger.GreatestCommonDivisor(b1, b2));

The System.Numerics.Complex type represents a complex number, in the form of a + bi, where a is the real part, and b is the imaginary part and allows you to

  • Compare two complex numbers to determine equality.
  • Perform arithmetic operations, such as addition, subtraction, multiplication, and division; other numerical operations, such as raising a complex number to a specific power; finding the square root or getting the absolute value; and trigonometric operations, such as calculating the cosine of an angle represented by a complex number.

Listing 3.3 shows some of the ways you can use the Complex type.

Listing 3.3. Working with Complex

Complex c1 = new Complex(10, 2);
Complex c2 = 3.14;
Complex c3 = Complex.FromPolarCoordinates(5, 0.25);
Complex c4 = (Complex)10.2m;

Console.WriteLine(c1);
Console.WriteLine(c2);
Console.WriteLine(Complex.Sqrt(c3));
Console.WriteLine(Complex.Exp(c4));
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