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With Beginning Visual C#, you will learn how to use Visual C# from first principles. Visual C# is an object-oriented programming language designed specifically for programming Microsoft's new platform, the .NET Framework. You'll quickly and easily learn how to write Visual C# code and create your own applications — for both Windows and the Web.
What does this book cover?
With clear explanations and hands-on examples, you will learn about the following topics:
This book will be an indispensable guide as you learn to write C# programs, gradually explaining the key concepts of Visual C# and .NET as your skills develop, with exercises at the end of chapters to test yourself. Starting with a thorough tutorial of the Visual C# language and object-oriented programming, you will progress to learn how to apply your understanding to programming the .NET Framework.
Who is this book for?
Beginning Visual C# is ideal for beginners with little background in programming, and for relatively inexperienced programmers who want to move from a language that doesn't support object-oriented programming techniques. The book moves at a fast enough pace that if you have programmed in another language, then you will still find the book valuable.
What do you need to use this book?
Note that Beginning Visual C# requires you to have access to either Visual Studio .NET or Visual C# .NET Standard Edition.
Chapter 1: Introducing C#.
Chapter 2: Writing a C# Program.
Chapter 3: Variables and Expressions.
Chapter 4: Flow Control.
Chapter 5: More About Variables.
Chapter 6: Functions.
Chapter 7: Debugging and Error Handling.
Chapter 8: Introduction to Object-Oriented Programming.
Chapter 9: Defining Classes.
Chapter 10: Defining Class Members.
Chapter 11: More About Classes.
Chapter 12: Events.
Chapter 13: Using Windows Form Controls.
Chapter 14: Advanced Windows Forms Features.
Chapter 15: Using Common Dialogs.
Chapter 16: Introduction to GDI+.
Chapter 17: Deploying Windows Applications.
Chapter 18: Getting At Your Data.
Chapter 19: Data Access with ADO.NET.
Chapter 20: Working With Files.
Chapter 21: .NET Assemblies.
Chapter 22: Attributes.
Chapter 23: ASP.NET Applications.
Chapter 24: Web Services.
Appendix A: Setting the PATH Environment Variable.
Appendix B: Installing MSDE.
Appendix C: Further References.
Welcome to the first chapter of the first section of this book. Over the course of this section we'll be taking a look at the basic knowledge required to get up and running. In this first chapter we'll be looking at an overview of C# and the .NET Framework, and we'll consider what these technologies are, the motivation behind using them, and how they relate to each other.
We'll start with a general discussion of the .NET Framework. This is a new technology, and contains many concepts that are tricky to get to grips with at first (mainly because the Framework introduces a "new way of doing things" to application development). This means that the discussion will, by necessity, cover many new concepts in a short space of time. However, a quick look at the basics is essential to understand how to program in C#, so this is a necessary evil. Later on in the book we'll revisit many of the topics covered here in more detail.
After this discussion, we'll move on to a simple description of C# itself, including its origins and similarities to C++.
Finally, we'll look at the main tool that will be used throughout this book: Visual Studio .NET (VS).
What is the .NET Framework?
The .NET Framework is a new and revolutionary platform created by Microsoft for developing applications.
The most interesting thing about this statement is how vague I've been - but there are good reasons for this. For a start, note that I didn't say "developing applications on the Windows operating system". Although the first release of the .NET Framework runs on the Windows operating system, future plans include versions that will work on others, such as FreeBSD, Linux, Macintosh, and even personal digital assistant (PDA) class devices. One of the key motivational forces behind this technology is its intention as a means of integrating disparate operating systems.
In addition, the definition of the .NET Framework given above includes no restriction on the type of applications that are possible. This is because there is no restriction - the .NET Framework allows the creation of Windows applications, web applications, web services, and pretty much anything else you can think of.
The .NET Framework has been designed such that it can be used from any language. This includes the subject of this book, C#, as well as C++, Visual Basic, JScript, and even older languages such as COBOL. In order for this to work, .NET-specific versions of these languages have also appeared: Managed C++, Visual Basic .NET, JScript .NET, J#, and so on - and more are being released all the time. Not only do all of these have access to the .NET Framework, they can also communicate with each other. It is perfectly possible for C# developers to make use of code written by Visual Basic .NET programmers, and vice versa.
All of this provides a hitherto unthinkable level of versatility, and is part of what makes using the .NET Framework such an attractive prospect.
What's in the .NET Framework?
The .NET Framework consists primarily of a gigantic library of code that we use from our client languages (such as C#) using object-oriented programming (OOP) techniques. This library is categorized into different modules - we use portions of it depending on the results we want to achieve. For example, one module contains the building blocks for Windows applications, another for network programming, and another for web development. Some modules are divided into more specific sub-modules, such as a module for building web services within the module for web development.
The intention here is that different operating systems may support some or all of these modules, depending on their characteristics. A PDA, for example, would include support for all the core .NET functionality, but is unlikely to require some of the more esoteric modules.
Part of the .NET Framework library defines some basic types. A type is a representation of data, and specifying some of the most fundamental of these (such as "a 32-bit signed integer") facilitates interoperability between languages using the .NET Framework. This is called the Common Type System (CTS).
As well as supplying this library, the framework also includes the .NET Common Language Runtime (CLR), which is responsible for maintaining the execution of all applications developed using the .NET library.
How do I Write Applications using the .NET Framework?
Writing an application using the .NET Framework means writing code (using any of the languages that support the framework) using the .NET code library. In this book we'll be using VS for our development, which is a powerful integrated development environment that supports C# (as well as managed and unmanaged C++, Visual Basic .NET, and some others). The advantage of this environment is the ease with which .NET features may be integrated into our code. The code that we will create will be entirely C#, but will use the .NET Framework throughout, and we'll make use of the additional tools in VS where necessary.
In order for C# code to execute it must be converted into a language that the target operating system understands, known as native code. This conversion is called compiling code, an act that is performed by a compiler. Under the .NET Framework, however, this is a two-stage process.
MSIL and JIT
When we compile code that uses the .NET Framework library, we don't immediately create operating system-specific native code. Instead, we compile our code into Microsoft Intermediate Language (MSIL) code. This code isn't specific to any operating system, and isn't specific to C#. Other .NET languages - for example, Visual Basic .NET - also compile to this language as a first stage. This compilation step is carried out by VS when we use it to develop C# applications.
Obviously, in order to execute an application more work is necessary. This is the job of a Just-In-Time (JIT) compiler, which compiles MSIL into native code that is specific to the OS and machine architecture being targeted. Only at this point can the OS execute the application. The "just-in-time" part of the name here reflects the fact that MSIL code is only compiled as and when it is needed.
In the past it has often been necessary to compile your code into several applications, each of which targets a specific operating system and CPU architecture. Often, this was a form of optimization (in order to get code to run faster on an AMD chipset, for example), but at times it was critical (for applications to work on both Win9x and WinNT/2000 environments, for example). This is now unnecessary, as JIT compilers (as their name suggests) use MSIL code, which is independent of the machine, operating system, and CPU. Several JIT compilers exist, each targeting a different architecture, and the appropriate one will be used to create the native code required.
The beauty of all this is that it requires a lot less work on our part - in fact we can just forget about system-dependent details, and concentrate on the more interesting functionality of our code.
When we compile an application, the MSIL code created is stored in an assembly. Assemblies include both executable application files that we can run directly from Windows without the need for any other programs (these have a .exe file extension), and libraries for use by other applications (which have a .dll extension).
As well as containing MSIL, assemblies also contain meta information (that is, information about the information contained in the assembly, also known as metadata) and optional resources (additional data used by the MSIL, such as sound files and pictures). The meta information allows assemblies to be fully self-descriptive. We need no other information in order to use an assembly, meaning that we avoid situations such as failing to add required data to the system registry and so on, which was often a problem when developing using other platforms.
This means that deploying applications is often as simple as copying the files into a directory on a remote computer. Since no additional information is required on the target systems, we can just run an executable file from this directory and (assuming the .NET CLR is installed) away we go.
Of course, we won't necessarily want to include everything required to run an application in one place. We might write some code that performs tasks required by multiple applications. In situations like this, it is often useful to place this reusable code in a place accessible to all applications. In the .NET Framework, this is the Global Assembly Cache (GAC). Placing code in this cache is simple - we just place the assembly containing the code in the directory containing this cache.
The role of the CLR doesn't end once we have compiled our code to MSIL and a JIT compiler has compiled this to native code. Code written using the .NET Framework is managed when it is executed (this stage is usually referred to as being at "runtime"). This means that the CLR looks after our applications, by managing memory, handling security, allowing cross-language debugging, and so on. By contrast, applications that do not run under the control of the CLR are said to be unmanaged and certain languages such as C++ can be used to write such applications, that, for example, access low-level functions of the operating system. However, in C# we can only write code that runs in a managed environment. We will make use of the managed features of the CLR and allow .NET itself to handle any interaction with the operating system.
One of the most important features of managed code is the concept of garbage collection. This is the .NET method of making sure that the memory used by an application is freed up completely when the application is no longer in use. Prior to .NET this has mostly been the responsibility of programmers, and a few simple errors in code could result in large blocks of memory mysteriously disappearing as a result of being allocated to the wrong place in memory. This usually meant a progressive slowdown of your computer followed by a system crash.
.NET garbage collection works by inspecting the memory of your computer every so often, and removing anything from it that is no longer needed. There is no set timeframe for this, it might happen thousands of times a second, once every few seconds, or whenever, but you can rest assured that it will happen.
There are some implications for programmers here. Since this work is done for you at an unpredictable time applications have to be designed with this in mind. Code that requires a lot of memory to run should tidy itself up rather than waiting for garbage collection to happen, but this isn't anything like as tricky as it sounds.
Fitting it Together
Before moving on, let's summarize the steps required to create a .NET application as discussed above:
1. Application code is written using a .NET-compatible language such as C#:
2. This code is compiled into MSIL, which is stored in an assembly:
3. When this code is executed (either in its own right if it is an executable, or when it is used from other code) it must first be compiled into native code using a JIT compiler:
4. The native code is executed in the context of the managed CLR, along with any other running applications or processes:
There is one additional point to note concerning the above process. The C# code that compiles into MSIL in step 2 needn't be contained in a single file. It is possible to split application code across multiple source code files, which are then compiled together into a single assembly. This process is known as linking, and is extremely useful. The reason for this is that it is far easier to work with several smaller files that one enormous one. You can separate out logically related code into an individual file, so that it can be worked on independently, and then practically forgotten about when completed. This also makes it much easier to locate specific pieces of code when you need them, and enables teams of developers to divide up the programming burden into manageable chunks, where individuals can "check out" pieces of code to work on without risking damage to otherwise satisfactory sections, or sections that other people are working on.
What is C#?
C#, as mentioned above, is one of the languages that can be used to create applications that will run in the .NET CLR. It is an evolution of the C and C++ languages and has been created by Microsoft specifically to work with the .NET platform. As it is a recent development, the C# language has been designed with hindsight, taking into account many of the best features from other languages while clearing up their problems.
Developing applications using C# is simpler than using C++, as the language syntax is simpler. However, C# is a powerful language and there is little we might want to do in C++ that we can't do in C#. Having said that, those features of C# which parallel the more advanced features of C++, such as directly accessing and manipulating system memory, can only be carried out using code marked as unsafe. This advanced programmatic technique is potentially dangerous (hence its name), as it is possible to overwrite system-critical blocks of memory with potentially catastrophic results. For this reason, and others, we are not going to cover this topic in this book.
At times, C# code is slightly more verbose than C++. This is a consequence of C# being a type-safe language (unlike C++). In layman's terms, this means that once some data has been assigned to a type, it cannot subsequently transform itself into another unrelated type. Consequently, there are strict rules that must be adhered to when converting between types, which means that we will often need to write more code to carry out the same task in C# as we might do in C++, but we get the benefit that code is more robust and debugging is simpler - .NET can always track what type a piece of data is at any time. In C# we therefore may not be able to do things such as "take the region of memory 4 bytes into this data and 10 bytes long and interpret it as X", but that's not necessarily a bad thing.
C# is just one of the languages available for .NET development, but in my opinion it is certainly the best. It has the advantage of being the only language designed from the ground-up for the .NET Framework and may be the principal language used in versions of .NET that are ported to other operating systems. To keep languages such as Visual Basic .N
Excerpted from Beginning Visual C# by Karli Watson David Espinosa Zach Greenvoss Jacob Hammer Pedersen Christian Nagel Jon D. Reid Matthew Reynolds Morgan Skinner Eric White Excerpted by permission.
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