Home > Articles > Programming > Windows Programming

.NET Languages

This sample chapter describes C# and Visual Basic.NET, the most important CLR-based languages. It also takes a brief look at the Managed Extensions for C++ that allow C++ developers to write CLR-based code. David Chappell's goal is to give you a sense of how these languages look and of how they express the core functionality provided by the CLR.
Purchase this book through the end of January and receive four exclusive sample chapters from forthcoming books by some of technology's greatest luminaries. For more information, check http://www.expectsomethingbetter.com.
This chapter is from the book

The Common Language Runtime is explicitly designed to support multiple languages. In general, though, languages built on the CLR tend to have a good deal in common. By defining a large set of core semantics, the CLR also defines a large part of a typical programming language built using it. For example, a substantial chunk of learning any CLR-based language is seeing how the standard types defined by the CLR are mapped into that language. You must also learn the language's syntax, of course, including the control structures the language provides. Yet once you know what the CLR offers, you're a long way down the path to learning any language built on top of it.

This chapter describes C# and Visual Basic.NET, the most important CLR-based languages. It also takes a brief look at the Managed Extensions for C++ that allow C++ developers to write CLR-based code. The goal is not to provide exhaustive coverage of every language feature—that would require three more books—but rather to give you a sense of how these languages look and of how they express the core functionality provided by the CLR.

What about Java for the .NET Framework?

In the fall of 2001, Microsoft announced Visual J#.NET, an implementation of the Java language built on the CLR. Despite this, I doubt that Java will ever be a viable choice for the .NET Framework. The reason is that even if a Java aficionado chooses to use a CLR-based Java compiler, such as Visual J#.NET, she's unlikely to be truly happy. Java implies a group of libraries and interfaces such as Swing and Enterprise JavaBeans. The .NET Framework provides its own equivalent technologies, and so most of these won't be available. As a result, a developer using the Java language on the .NET Framework won't feel like she's working in a true Java environment because the familiar libraries won't be there.

The real target market for Visual J#.NET is Microsoft's existing Visual J++ customers. By providing a migration path to the .NET Framework, Microsoft is helping them move away from a dying platform to one with a long future ahead of it. People who believe that Microsoft is truly interested in building a first-class environment for building new Java applications might also wish to examine their beliefs about Santa Claus.

The battle lines are clear: It's .NET versus the Java world. This is unquestionably a good thing. Those who think everyone should implement Java forget both the dangers of monopoly and the sloth that comes with having no competition. Having two powerful technology camps, each with a strong position, is the ideal world. Each has innovations that the other can learn from, and each provides examples of things to avoid. In the end, the competition makes both of them better.

C#

As its name suggests, C# is a member of the C family of programming languages. Unlike C, C# is explicitly object-oriented. Unlike C++, however, which is the most widely used object-oriented language in this family, C# isn't fiendishly complicated. Instead, C# was designed to be easily approachable by anyone with a background in C++ or Java.

The most popular tool today for creating C# code is Microsoft's Visual Studio.NET. It's not the only choice, however. Microsoft also provides a command-line compiler with the .NET

Framework called csc.exe, and the open source world has also created a C# compiler. Visual Studio.NET provides a rich environment for building CLR-based applications in C#, however, so it's hard to imagine that other alternatives will attract a large share of developers.

Standardizing C# and the CLR

Microsoft has submitted C# and a subset of the CLR called the Common Language Infrastructure (CLI) to the international standards body ECMA, where they are on track to become ECMA standards. Along with C#, the things that have been submitted for standardization include the syntax and semantics for meta-data, MSIL (rechristened the Common Intermediate Language, or CIL), and parts of the .NET Framework class library. For more details on exactly what has been submitted and its current status, see msdn.microsoft.com/net/ecma.

Sun came close to doing something similar with its Java technology, but backed away at the last minute. Will Microsoft's efforts be more successful? Sun resisted this step in large part because they were unwilling to give up control of Java. Control of Java is a valuable thing, and since Sun is a for-profit company, its reluctance to relinquish this control makes perfect sense. Microsoft is also a for-profit company. Will they really wait until ECMA has approved, say, an enhancement to C# before including it in their next release? And if they do, is this a good thing? Standards bodies aren't known for their speed.

I'd be surprised if Microsoft lets ECMA control the rate at which innovations appear in future releases of .NET technologies. Still, making C# and the CLI standards does give others a way to build them. Somewhat surprisingly, given its traditional antipathy toward Microsoft, the open source world has spawned various efforts to build parts of .NET. The most visible of these is the Mono project. (Mono means "monkey" in Spanish, which may be an oblique commentary on the Mono team's view of Microsoft.) Mono's ambitious goal is to implement at least a large part of what Microsoft has given to ECMA, including a C# compiler and the CLI, and perhaps more. Mono's creators say that they were attracted to the CLR for technical reasons, which must please Microsoft. In fact, from Mono's perspective, the CLI is the specification of a system while .NET's CLR is just the Microsoft implementation of this specification. Mono is certainly an interesting undertaking; to learn more about it, see http://www.go-mono.com.

Microsoft itself, together with Corel, has announced plans to make an implementation of C# and the CLI available for BSD UNIX. As discussed in Chapter 1, Microsoft faces substantial credibility problems in porting the .NET Framework to non-Windows platforms. Still, it's early in the game, and anything is possible. Whatever happens, having public standards and an open source implementation for their core technologies will certainly be a new experience for Microsoft.

A C# Example

Like most programming languages, C# defines data types, control structures, and more. Unlike older languages, however, C# does this by building on the CLR. Understanding the CLR therefore takes one a long way toward understanding C#. To illustrate this, here's a simple C# example:

// A C# example 
interface IMath 
{ 
     int Factorial(int f); 
     double SquareRoot(double s); 
} 
class Compute : IMath 
{
      public int Factorial(int f) 
     { 
          int i; 
          int result = 1; 
          for (i=2; i<=f; i++)
                 result = result * i; 
          return result; 
      } 
      public double SquareRoot(double s) 
     { 
           return System.Math.Sqrt(s); 
      } 
} 
class DisplayValues 
{ 
      static void Main() 
      { 
           Compute c = new Compute(); 
            int v; 
            v = 5; 
   System.Console.WriteLine("{0} factorial: 
       {1}", v, c.Factorial(v)); 
   System.Console.WriteLine("Square root of {0}: 
       {1:f4}", v, c.SquareRoot(v)); 
      } 
} 

The program begins with a comment, indicated by two slashes, giving a brief description of the program's purpose. The body of the program consists of three types: an interface named IMath and the two classes Compute and DisplayValues. All C# programs consist of some number of types, the outermost of which must be classes, interfaces, structures, enums, or delegates. (Namespaces, discussed later, can also appear here.) All methods, fields, and other type members must belong to one of these types, which means that C# doesn't allow either global variables or global methods.

The IMath interface, which is a C# incarnation of the Common Type System (CTS) interface type described in Chapter 3, defines the methods Factorial and SquareRoot. Each of these methods takes one parameter and returns a numeric result. These parameters are passed by value, the default in C#. This means that changes made to the parameter's value within the method won't be seen by the caller once the method returns. Placing the keyword ref in front of a parameter causes a parameter to be passed by reference, so any changes made within the method will be reflected back to the caller.

Each class in this example is also a C# incarnation of the underlying CTS type. C# classes can implement one or more interfaces, inherit from at most one other class, and do all of the other things defined for a CTS class. The first class shown here, Compute, implements the IMath interface, as indicated by the colon between Compute and IMath. Accordingly, this class must contain implementations for both of the interface's methods. The body of the Factorial method declares a pair of integer variables, initializes the second of them to 1, then uses a simple for loop to calculate the factorial of its parameter (and doesn't bother to check for overflow, which is admittedly bad programming practice). Compute's second method, SquareRoot, is even simpler. It relies on the .NET Framework class library, calling the Sqrt function provided by the Math class in the System namespace.

The last type in this simple example, the class DisplayValues, contains only a single method named Main. Much like C and C++, a C# program begins executing with this method in whatever type it appears. Although it's not shown here, Main can take arguments passed in when the program is started, and it must be declared as static. In this example, Main returns void, which is C#'s way of saying that the method has no return value. The type void cannot be used for parameters as in C and C++, however. Instead, its only purpose is to indicate that a method returns no value.

In this example, Main creates an instance of the Compute class using C#'s new operator. When this program is executed, new will be translated into the MSIL instruction newobj described in the Chapter 3. Main next declares an int variable and sets its value to 5. This value is then passed as a parameter into calls to the Factorial and SquareRoot methods provided by the Compute instance. Factorial expects an int, which is exactly what's passed in this call, but SquareRoot expects a double. The int will automatically be converted into a double, since this conversion can be done with no loss of information. C# calls this an implicit conversion, distinguishing it from type conversions that are marked explicitly in the code.

The results are written out using the WriteLine method of the Console class, another standard part of the .NET Framework's System namespace. This method uses numbers wrapped in curly braces that correspond to the variables to be output. Note that in the second call to WriteLine, the number in braces is followed by ":f4". This formatting directive means that the value should be written as a fixed-point number with four places to the right of the decimal. Accordingly, the output of this simple program is

5 factorial: 120 
Square root of 5: 2.2361 

The goal of this example is give you a feeling for the general structure and style of C#. There's much more to the language, as the next sections illustrate.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020