C# & OOPs

What is a Class?

A class is a blueprint or prototype that defines the variables and the methods (functions) common to all objects of a certain kind.

What is an Object?

An object is a representative or specimen of a class. Software objects are often used to model real-world objects you find in everyday life.
For example :

Features of OOPs :

1. Abstraction is the process of exposing the relevant things and hiding the irrelevant details. The easiest way to understand and appreciate this concept of handling complexity is by studying the example of Globe, a model/prototype of earth that is used by students to understand its geography. Globe provides only that information that is required and if too much of information is mentioned in it i.e. streets, lakes etc, it becomes too complex to comprehend. Hence Globe abstracts unwanted information and makes it easy to comprehend the complex earth.

2. Encapsulation is the mechanism that binds together code and the data it manipulates, and keeps both safe from outside interference and misuse. The data is not accessible to the outside world and only those functions that are wrapped in the class can access it. These functions provide the interface between the object’s data and the program. The insulation of the data from the direct access by the program is called data hiding.
   In OOP, code and data are merged into an object so that the user of an object can never peek inside the box. This is defined as encapsulation (Object is a capsule encapsulating data and behavior). All communication to it is through messages (function calls which we use to communicate to the object). Messages define the interface to the object. Everything an object can do is represented by its message interface. Therefore, we need not know anything about what is in the object when we use it.

3. Inheritance is the process by which one class acquires the properties and functionalities of another class. This is important because it supports the concept of hierarchical classification.. Inheritance provides the idea of reusability of code and each sub class defines only those features that are unique to it.

4. Polymorphism is a feature that allows one interface to be used for a general class of actions. An operation may exhibit different behavior in different instances. The behavior depends on the types of data used in the operation. It plays an important role in allowing objects having different internal structures to share the same external interface. Polymorphism is extensively used in implementing inheritance.
   Ex:
   add(int a, int b)
   add(int a, float b, int c)
   add(int a, int b, float c, double d)
   Here different datatypes are being added using the same interface.

Features of C#

•Object-oriented

•Simpler language

−Compared to earlier OO languages like C++, it is simple

−Designed considering the pitfalls of earlier languages

•Robust

•Architecture Neutral / Portable

•Secure

−Built -in security features like absence of pointers and confinement of the C# program within its runtime environment

•Support for Multithreading at language level

•Designed to handle Distributed applications

Structure of C# Program

using System;
class FirstProgram
{
public static void Main()
{
Console.WriteLine(“Hello World”);
}
}

•The extension of a C# program is cs

•There is no restriction on the filename unless it follows the naming convention of the OS

•Every statement in C# ends with ;

•Main is the starting point of execution of a C# program

•{ } describes a block of code

•Main function must be written inside the class