Static

Static keyword has different role in different places for C#. When we declare static that means only single copy will be generate.

Static container can only contains static members

It is used in below places-

• Class
• Method
• Field
• Properties
• Constructor

Static Class

• Only contain all static members like static methods, static fields, static properties and static constructor.
• Any instance or non-static member can not be there in the Static Class.
• If we need to create all the members as static then we can create static class.
• Can not create instance of such class.
• Sealed.
• Cannot contain Instance Constructors

Static Methods

• Only contain all static fields
• Non-static fields are not allowed in static methods
• Method can be access using class only, no instance is needed or can access.
• Single copy of static method will be shared among all the instances.

Static Fields

• Single copy of fields/variables get created and shared among all the instances.
• If static variable value has been change using one instance then all other instance will get that changed value.

Static Property

• Can be access using class only.
• Using instance it can not be access.

Static Constructor

• Access modifier are not allowed.
• Static Constructor as it(class constructor) execute prior to any other constructor (instance constructor).
• Can instantiate value of static fields only.
• Non-Static fields is not allowed within the scope.

More About Static:

• Static methods are not allowed in the interface.
• Access modifiers are not allowed in the interface and static constructor.
• Static class can't be inherit from interface/class/static class.
• Static class can only be inherit from object. ??
• Inheritance from static class in not possible as static classes are sealed.
• Inherited Static method can not be marked as override, virtual or abstract.
• Inherited Static methods can be marked as new.

Structured/Imperative/Functional/Procedural Programming

Structured Programming 

• Top-down analysis
• Problem broken down into small piece (sub-problems) where each one has some significance.
• Each small piece of problems are individually solved and steps are clearly stated.
• Modular Programming
• Code is broke down into small groups of instructions
• These groups are knows as modules or subprograms or subroutines or methods.
• Avoid jumps (unconditional GoTo) as non-traceable
• Structured Code
• Divide modules into further small units of code

• Follow Top Down design model 
• Maintainable Code
• Systematic Organization
• Reusable code block
• Subdivision of program into functions
• Hierarchy of task
• Simple and easy to understand the code
• Avoid unconditional Goto

Un-Structured code

• Unconditional Goto 

Imperative languages

• Imperative programming is a paradigm of computer programming in which the program describes a sequence of steps that change the state of the computer.
• Unlike declarative programming, which describes "what" a program should accomplish, imperative programming explicitly tells the computer "how" to accomplish it.
• To make programs simpler for a human to read and write, imperative statements can be grouped into sections known as code blocks.

Functional Programming

• Functional programming (FP) is about passing data from function to function to get a result.
• In FP, functions are treated as data, meaning you can use them as parameters, return them, build functions from other functions, and build custom functions.
• A functional approach involves composing the problem as a set of functions to be executed.
• In software, everything is a statement, unless it is a function. 

Procedural Programming

• Procedural programming is a programming paradigm, derived from structured programming
• Based upon the concept of the procedure call. Procedures
• Also known as routines, subroutines, or functions, simply contain a series of computational steps to be carried out.
• Any given procedure might be called at any point during a program's execution, including by other procedures or itself.
• Procedural programming (PP), also known as inline programming takes a top-down approach.
• It is about writing a list of instructions to tell the computer what to do step by step.
• It relies on procedures or routines.
• Procedural programming is a type of imperative programming in which the program is built from one or more procedures (also termed subroutines or functions).
• Procedural programming could be considered a step towards declarative programming.
• A programmer can often tell, simply by looking at the names, arguments, and return types of procedures (and related comments), what a particular procedure is supposed to do, without necessarily looking at the details of how it achieves its result.
• At the same time, a complete program is still imperative since it fixes the statements to be executed and their order of execution to a large extent.