Introduction to C# Programming

• C# is an object-oriented programming language, supporting data encapsulation, inheritance, polymorphism, and method overriding.
• Anders Hejlsberg led the development of C# at Microsoft in the late 1990s..
• C# can be used to build web, Windows, mobile, and cloud-based applications.

C# Features

• Develop both console and web applications with C#.
• C# supports garbage collection and automatic memory management.
• Native support for Component Object Model (COM) and Windows-based applications is included in C#.
• Primitive data types are automatically initialized to zeros, while reference types are initialized to null in C#.
• C# produces portable code that executes in a secure, controlled runtime environment.
• Generics, partial types, and anonymous methods are all supported by C#.
• Language-integrated query (LINQ) and lambda expressions are supported to enable database queries and efficient coding.

.NET Framework Structure

• The .NET framework contains tools, technologies, and languages for building and deploying different types of applications.
• The .NET framework is a software development framework from Microsoft.
• Key components include VB, C++, C#, JScript, J#, Common Language Specification, ASP.NET (Web Forms, Web Services, Windows Forms), ADO.NET and XML, Base Class Library, Common Language Runtime, and the Operating System.
• The operating system manages system resources.
• It runs on Microsoft OS, but has alternatives for other OS.
• Common Language Runtime (CLR) manages the execution of .NET code, allowing for debugging, exception handling, and portability.
• CLR converts source code into Microsoft Intermediate Language (MSIL).
• The CLR Just-In-Time (JIT) compiler compiles the MSIL code into native (machine-language) code.
• The .NET Base Class Library contains the classes and interfaces used for building applications, organized as namespaces.
• Namespaces are included in programs, and these .NET objects can build and interact with ASP.NET, Windows Forms, and/or ADO.NET and XML.
• ADO.NET provides access to relational databases and data sources - SQL Server and XML.
• XML is the universal format for data on the Web.
• ASP.NET is a web development model for building enterprise-class web applications with minimal coding
• ASP.NET Web Forms allow building dynamic websites with a drag-and-drop, event-driven model.
• ASP.NET Web Services extend the Web infrastructure for software to connect to other applications.
• Windows Forms contain the graphical representation of any window displayed in the application.
• Common Language Specification (CLS) ensures operability between languages in the .NET environment, as a subset of CTS.
• Common Type System (CTS) is a formal specification that documents how types are declared, used, and managed so the CLR can use them.
• VB, C++, C#, Jscript, and J# are languages supported by .NET.

NET supports the following features

• NET includes a large library and supports several programming languages for code in different languages.
• Code in supported languages compiles into Common Language Infrastructure (CLI), enabling the exchange of data types between programs.
• NET supports AJAX for creating highly responsive web applications with minimal effort.
• NET uses assembly for code sharing, allowing only authorized users or processes to call designated methods.
• Also supported are Common Language Runtime, Development for dynamic Web pages, Base Class Library, ADO.NET, and Web services.

Assembly Use

• An assembly is a collection of types and resources built to work together as a logical unit of functionality and are the building blocks of .NET framework applications.
• Assemblies form the unit of deployment, version control, reuse, activation scoping, and security permissions.
• Applications in .NET are deployed as an assembly consisting of compiled code containing code that CLR executes.
• .NET code on compilation converts into intermediate language code as an assembly, in the form of EXE (executable) or DLL (Dynamic-Link Library), with DLL containing functions and data usable by other modules or applications.
• Assemblies contain metadata with information and descriptions of methods, types, and other resources, including a Manifest.
• Manifest stores identification information, public types, and an assembly list.
• Each assembly has a 128-bit version number, presented as Major.Minor.Build.Revision (e.g., 8.0.1.7).
• Versioning allows developers to install versions of components that are not backward compatible.
• Assemblies can be deployed as private or shared.
• Multiple applications can use a shared assembly, but only a single application can use a private assembly.
• Shared assemblies must be registered in the Global Assembly Cache (GAC), while private assemblies are stored in the application's directory and do not need registration.
• A strong name is required for a shared assembly, but not for a private one.
• Shared assemblies can support multiple versions that are not backward compatible, but a private assembly with multiple versions that are not backward compatible will cause the application to stop.
• All created assemblies are considered private by default until registered in GAC with a strong name, then it becomes a shared assembly.

Program Structure of C#

• A C# program consists of namespace declaration, class attributes, comments, a class, a Main method, class methods, and statements and expressions.
• Namespaces organize classes in a project, and a namespace declaration is a collection of classes.
• System is is a namespace and Console is a class of System.
• The using keyword accesses classes in a namespace and must appear at the beginning of a source code, which is saved as a class name with .cs extension.
• Statements enclosed in /*...*/ and // are comments ignored by the compiler.
• Every C# application has one Main method, which is the starting point of every application containing the statements that will be executed.
• In the example program, the static void Main (string[] args) {} takes string array as an argument and must be defined in the class as the static method.
• The Main method contains the statements and expressions that will be executed when the program is compiled, and all statements and expressions in C# end with a semicolon (;).