Intro To C

What is the Difference Between C# and .NET?

C# is a programming language. .NET is a framework for building applications on Windows. .NET uses C#, but there are other languages like F# and VB.NET too.

.NET consists of 2 components: Common Language Runtime or CLR and a class library for building apps.

What is CLR?

Before C#, we had C and C++. With either of these languages, the compiler translated our code into the native code for the machine running. However, if we were to run that same native code compiled in a different machine/architecture, it wouldn't run.

C# was born from a design choice made in java. Instead of compiling down to machine code and running into the problem of machine specificity, java compiles down to byte code.

In C#, our byte code is called IL code or intermediate language code. This is code that is independent of the machine it's running on.

CLR then translates the IL code into native code for the machine it's running on. This is called a just-in-time compilation approach (also called JIT): the code is compiled by the machine for the machine right when it needs it. And as long as the machine has CLR installed, C# works.

The Architecture of .NET Applications

When you build an application in C#, your application consists of building blocks called classes.

Classes

Classes have data called attributes and functions called methods.

Namespaces

As the number of classes grows (they can grow the 100s in applications), we use namespaces to organize them.

A namespace is a container for related classes.

These namespaces could be for:

• Databases

• Graphics and images

• Security

• Etc.

Assembly

Even higher level, applications also have assemblies. An assembly is a container for related namespaces.

Physically, an assembly is a file: either a DLL or EXE. A DLL is a file that includes code that can be reused across different programs. An EXE is a file that can be executed.

Common Files in C# Application

• Properties/AssemblyInfo.cs

  • Identification for the assembly file that gets produced when your C# application gets compiled (title, description, company, etc.)

• References directory

  • These are any assemblies that the project references and uses

• App.config

  • XML where configuration is set up (example: SQL connection strings)

• Program.cs

  • At the top, there are using X statements where we import code from other assemblies/namespaces

  • There is also usually a class Program with a Main function that acts the entry point to the application (when you run your application, Main execute)