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Object Orientation

Object Orientation (OO) is a programming paradigm that organizes software into objects that contain both data (properties) and behavior (methods). It helps developers write reusable, secure, and maintainable programs.

Object-oriented programming (OOP) is the foundation of C#. Instead of writing long procedural code, programs are divided into objects that interact with each other. C# supports the four pillars of OOP:

Encapsulation
Inheritance
Polymorphism
Abstraction

OOP Pillars

Encapsulation

Bundles data and methods into a single class.
Protects data from unauthorized access.

Example

class Student

{

public string Name;

public void Display()

{

Console.WriteLine(Name);

}

Real-World Scenario (Nepal)

A Khalti wallet stores a user’s balance privately. Users can access or modify it only through authorized functions like Load Money or Pay, not by directly changing the balance.

Diagram

Inheritance

Allows one class to acquire the properties and methods of another class.

Example

Vehicle

Car

A Car automatically gets common features from Vehicle.

Real-World Scenario (Nepal)

A Government Employee class can be inherited by Teacher, Police Officer, and Doctor, since all are government employees but have additional responsibilities.

Polymorphism

Allows one method to perform different tasks depending on the object.

Example

Draw()

Circle → Draw Circle

Rectangle → Draw Rectangle

Triangle → Draw Triangle

Abstraction

Shows only essential information while hiding implementation details.

Example

While using an ATM, users press buttons to withdraw money without knowing how the banking system processes the transaction.

Real-World Scenario (Nepal)

Using the eSewa mobile app. Users simply tap Pay Electricity Bill, while the application hides all backend processing.

Diagram

Advantages of OOP

Reusability
Easy maintenance
Better security
Modular programming
Reduced development time
Easy debugging
Scalability

Key Points for Exam

OOP is the foundation of C# programming.
Four pillars: Encapsulation, Inheritance, Polymorphism, and Abstraction.
Objects contain both data and methods.
OOP improves code reuse, security, and maintainability.

Type Safety

Type Safety is the feature of C# that prevents a variable from storing a value of an incompatible data type, reducing programming errors and improving program reliability.

C# is a strongly typed language. Every variable must have a declared data type, and the compiler checks type compatibility before execution.

Example

int age = 20;

string name = “Ram”;

Correct because the assigned values match the declared data types.

Invalid example:

int age = “Twenty”;

This produces a compile-time error because a string cannot be assigned to an integer.

Benefits of Type Safety

Detects errors during compilation.
Prevents invalid memory access.
Improves program reliability.
Makes debugging easier.
Enhances application security.

Compile-Time Type Checking

Real-World Scenario (Nepal)

In the National Identity Card Registration System, the Age field accepts only numeric values. If someone enters “Twenty” instead of 20, the system rejects the input before saving the record. This is similar to type safety in C#.

Key Points for Exam

C# is a strongly typed language.
Type safety prevents invalid assignments.
Most type errors are detected during compilation.
It increases software security and reliability.

Memory Management

Memory Management is the process of allocating and releasing memory automatically so that programs use system resources efficiently.

Unlike languages such as C++, C# automatically manages memory through the Garbage Collector (GC). Programmers generally do not need to free memory manually.

Types of Memory

Stack Memory

Stores local variables.
Fast memory allocation.
Automatically released when a method ends.

Heap Memory

Stores objects created using the new keyword.
Managed by the Garbage Collector.
Slower than stack memory.

Diagram

Garbage Collection (GC)

The Garbage Collector (GC) is a component of the CLR that automatically removes objects that are no longer used by the program, freeing heap memory.

Working Process

Example

Student s = new Student();

When s is no longer referenced, the Garbage Collector eventually removes the object from memory.

Advantages of Automatic Memory Management

Prevents memory leaks.
Reduces programming errors.
Improves application performance.
Simplifies development.
Eliminates manual memory deallocation.

Real-World Scenario (Nepal)

Consider a TU Online Admission Portal. Thousands of student records are processed every day. Once a request is completed, the temporary objects used for processing are automatically removed from memory by the Garbage Collector, allowing the server to continue handling new requests efficiently.

Difference Between Stack and Heap

Stack	Heap
Stores local variables	Stores objects
Faster	Comparatively slower
Automatically released after method execution	Released by Garbage Collector
Small memory	Large memory
LIFO structure	Dynamic memory allocation

Key Points for Exam

Memory management is automatic in C#.
Stack stores local variables; Heap stores objects.
Garbage Collector automatically frees unused heap memory.
Automatic memory management improves performance and prevents memory leaks.

Platform Support

Platform Support is the capability of C# and the .NET Framework to develop and execute applications on different operating systems and hardware platforms with minimal code changes.

Initially, the .NET Framework was designed for Windows. With the introduction of .NET Core and later .NET (5/6/7/8), C# applications became cross-platform and can run on Windows, Linux, and macOS.

Types of Platform Support

Windows
- Supports Windows Forms, WPF, ASP.NET, Console Applications, and Services.
Linux
- Supports Console Applications, ASP.NET Core, Cloud Applications, and Microservices.
macOS
- Supports Desktop, Console, and Web Applications using .NET.
Mobile Platforms
- Android and iOS applications can be developed using .NET MAUI or Xamarin.
Cloud Platforms
- Applications can be deployed on Microsoft Azure, AWS, and Google Cloud Platform.

Example

A developer creates an ASP.NET Core web application on Windows. The same application can be hosted on a Linux server without changing its source code.

Real-World Scenario (Nepal)

A software company in Kathmandu develops an online college management system using ASP.NET Core on Windows laptops. The system is later deployed to a Linux cloud server, allowing students and teachers across Nepal to access it through a web browser.

Diagram

Advantages of Platform Support

Code reusability across multiple operating systems.
Lower development and maintenance cost.
Easier deployment on cloud platforms.
Supports modern application development.

Key Points for Exam

Platform support enables applications to run on multiple operating systems.
Modern .NET is cross-platform.
ASP.NET Core is commonly used for cross-platform web development.

C# and CLR

Common Language Runtime (CLR) is the execution engine of the .NET Framework that manages the execution of C# programs by providing services such as memory management, security, exception handling, and garbage collection.

When a C# program is compiled, it is not converted directly into machine code. Instead, it is converted into Intermediate Language (IL). The CLR then uses the Just-In-Time (JIT) Compiler to convert IL into machine code during execution.

Program Execution Process

Responsibilities of CLR

Memory Management

Allocates memory for objects.
Removes unused objects using Garbage Collection.

Garbage Collection

Automatically frees memory occupied by unused objects.

Exception Handling

Detects and handles runtime errors.

Security

Verifies code before execution.
Prevents unauthorized access.

Thread Management

Supports execution of multiple threads simultaneously.

Language Interoperability

Allows different .NET languages (C#, VB.NET, F#) to interact.

Example

using System;

class Program

{

static void Main()

{

Console.WriteLine(“Hello, .NET”);

}

Execution Steps:

C# compiler converts the code into IL.
CLR loads the IL.
JIT Compiler converts IL into machine code.
The program executes.

Real-World Scenario (Nepal)

A banking application developed in C# by a financial institution in Nepal relies on the CLR to manage memory, protect sensitive customer data, and recover gracefully from runtime exceptions, ensuring reliable transactions.

Diagram

Advantages of CLR

Automatic memory management.
Platform independence through IL.
Improved security.
Better performance using JIT compilation.
Simplified exception handling.

Key Points for Exam

CLR is the execution engine of .NET.
C# code is first compiled into Intermediate Language (IL).
JIT Compiler converts IL into machine code.
CLR provides Garbage Collection, security, exception handling, and memory management.

CLR and .NET Framework

.NET Framework is a software development platform provided by Microsoft, while the Common Language Runtime (CLR) is its execution engine responsible for running .NET applications.

The .NET Framework provides libraries and APIs for application development, whereas the CLR executes the compiled code and manages runtime services.

Components of the .NET Framework

Common Language Runtime (CLR)

Executes .NET applications.
Manages memory and exceptions.
Performs JIT compilation.

Framework Class Library (FCL)

A collection of reusable classes.
Provides functionality for file handling, networking, collections, databases, security, and web development.

Languages Supported

C#
VB.NET
F#
Managed C++

Architecture of .NET Framework

CLR vs .NET Framework

CLR	.NET Framework
Runtime environment	Software development platform
Executes programs	Provides libraries and runtime
Performs JIT compilation	Contains CLR and FCL
Handles memory management	Used to build applications
Performs Garbage Collection	Supports multiple programming languages

Framework Class Library (FCL)

The Framework Class Library (FCL) is a collection of predefined classes and namespaces that simplify software development.

Common Namespaces

Namespace	Purpose
System	Basic classes
System.IO	File handling
System.Collections	Collections
System.Net	Networking
System.Data	Database programming
System.Web	Web applications

Example

using System;

class Program

{

static void Main()

{

DateTime today = DateTime.Now;

Console.WriteLine(today);

}

Here, the System namespace and DateTime class are provided by the Framework Class Library.

Real-World Scenario (Nepal)

A university develops an online examination system using the .NET Framework. The application uses:

System.Data for database operations.
System.IO for report generation.
CLR for runtime execution and memory management.

Diagram

Advantages of the .NET Framework

Rich library support.
Easy application development.
High security.
Automatic memory management.
Language interoperability.
Improved developer productivity.

Key Points for Exam

The .NET Framework consists mainly of the CLR and the Framework Class Library (FCL).
CLR executes programs and manages runtime services.
FCL provides reusable classes and namespaces.
C#, VB.NET, and F# can all run on the same CLR.

Other Frameworks

Other Frameworks are Microsoft and third-party .NET implementations that allow developers to build applications for different platforms such as desktop, web, cloud, and mobile devices.

Besides the traditional .NET Framework, Microsoft introduced several frameworks to overcome platform limitations and improve performance.

.NET Core

.NET Core is an open-source, cross-platform framework developed by Microsoft for building modern applications.

Unlike the traditional .NET Framework, .NET Core supports Windows, Linux, and macOS.

Features

Cross-platform
Open-source
High performance

/Max
Cloud-ready
Supports microservices
Command Line Interface (CLI)

Example

A developer creates an ASP.NET Core website on Windows and deploys it to a Linux server without modifying the source code.

Real-World Scenario (Nepal)

A startup in Kathmandu develops an online food delivery system using ASP.NET Core and hosts it on a Linux cloud server, reducing hosting costs while maintaining performance.

Mono

Mono is an open-source implementation of the .NET Framework that enables .NET applications to run on non-Windows platforms.

Mono was widely used before the release of .NET Core and is still used in some legacy applications.

Features

Cross-platform
Open-source
Supports Linux and macOS
Supports game development through Unity

Example

Unity game developers often use Mono to execute C# scripts during development.

Real-World Scenario (Nepal)

A game development company in Nepal uses Unity with Mono to build educational games for schools.

Xamarin

Xamarin is a Microsoft framework used to develop Android and iOS applications using C#.

Developers write one codebase that can be shared across multiple mobile platforms.

Features

Cross-platform mobile development
Native performance
Shared business logic
Visual Studio integration

Example

One C# application can run on both Android and iPhone.

Real-World Scenario (Nepal)

A hospital develops a mobile appointment system using Xamarin, allowing both Android and iPhone users to book appointments.

.NET MAUI

.NET Multi-platform App UI (MAUI) is the successor to Xamarin used for developing desktop and mobile applications from a single codebase.

Supported Platforms

Windows
Android
iOS
macOS

Diagram

Key Points for Exam

.NET Core is cross-platform and open-source.
Mono allows .NET applications to run on Linux and macOS.
Xamarin develops mobile applications.
.NET MAUI is the modern replacement for Xamarin.

Framework Overview

Framework Overview refers to the overall architecture and components of the .NET Framework that work together to develop and execute applications efficiently.

The .NET Framework provides a complete environment for software development by combining runtime services with reusable libraries.

Main Components

1. Common Language Runtime (CLR)

Responsible for:

Program execution
Memory management
Security
Garbage Collection
Exception handling

2. Framework Class Library (FCL)

Provides reusable classes for:

File handling
Networking
Database connectivity
XML processing
Collections
Security

3. Languages

Applications can be written using:

C#
VB.NET
F#
Managed C++

4. Applications

Using .NET, developers can build:

Console Applications
Windows Applications
Web Applications
Mobile Applications
Cloud Applications
APIs

Overall Architecture

Real-World Scenario (Nepal)

A university management system uses:

C# language
Framework Class Library
SQL Server database
CLR for execution

All these components work together to manage admissions, examinations, and result processing.

Key Points for Exam

The .NET Framework consists mainly of CLR and FCL.
Supports multiple programming languages.
Provides reusable libraries for rapid development.
Supports desktop, web, mobile, and cloud applications.

.NET Standard 2.0

.NET Standard 2.0 is a specification that defines a common set of APIs that all .NET implementations must support, ensuring code compatibility across different .NET platforms.

It is not a runtime or framework. Instead, it acts as a contract that allows developers to create reusable libraries.

Purpose

Improves code sharing
Increases compatibility
Simplifies library development
Reduces duplicate code

Supported Platforms

.NET Framework
.NET Core
Xamarin
Mono
.NET 5+
.NET MAUI

Diagram

Example

A class library developed using .NET Standard can be used by:

Desktop applications
Mobile applications
Web applications

without changing the source code.

Real-World Scenario (Nepal)

A software company develops a Student Library Management Library using .NET Standard. The same library is reused in desktop software, mobile applications, and web portals for multiple colleges.

Advantages

Platform independence
Code reusability
Easy maintenance
Improved compatibility

Key Points for Exam

.NET Standard defines APIs, not a runtime.
Enables sharing libraries across different .NET platforms.
Improves portability and maintainability.

Applied Technologies

Applied Technologies are real-world technologies and application areas where C# and the .NET platform are used to develop software solutions.

Desktop Applications

Developed using:

Windows Forms
WPF

Examples

Billing System
Payroll System
Inventory Management

Web Applications

Developed using:

ASP.NET
ASP.NET Core

Examples

E-commerce websites
Online examination systems
College management systems

Mobile Applications

Developed using:

Xamarin
.NET MAUI

Examples

Banking apps
Hospital management apps
Food delivery apps

Cloud Applications

Developed using:

Microsoft Azure
ASP.NET Core

Examples include:

Online storage
Cloud APIs
SaaS applications

Database Applications

Developed using:

ADO.NET
Entity Framework

Examples:

Banking systems
Student Information Systems
Hospital Management Systems

Game Development

Developed using:

Unity Game Engine
C#

Examples:

Educational games
Simulation games
2D and 3D games

Internet of Things (IoT)

Developed using:

.NET IoT Libraries

Examples:

Smart home automation
Smart agriculture
Weather monitoring

Diagram

Real-World Scenario (Nepal)

Many organizations in Nepal use .NET technologies:

Organization	Possible Application
Banks	Internet Banking System
Hospitals	Patient Management
Colleges	Student Management
Government Offices	Citizen Information Systems
E-commerce Companies	Online Shopping Platforms

Advantages of .NET Technologies

High security
Fast development
Cross-platform support
Rich Framework Class Library
Excellent database connectivity
Large developer community

Key Points for Exam

.NET is widely used for desktop, web, mobile, cloud, gaming, and database applications.
ASP.NET is used for web development.
ADO.NET and Entity Framework are used for database connectivity.
Unity uses C# for game development.

Important Terms to Remember

Object-Oriented Programming (OOP)
Type Safety
Memory Management
Stack Memory
Heap Memory
Garbage Collector (GC)
Common Language Runtime (CLR)
Intermediate Language (IL)
Just-In-Time (JIT) Compiler
Framework Class Library (FCL)
.NET Framework
.NET Core
Mono
Xamarin
.NET MAUI
.NET Standard 2.0
ASP.NET
ADO.NET

Frequently Asked TU Examination Questions

Short Questions (5 Marks)

Define Object-Oriented Programming. Explain its four pillars.
What is Type Safety in C#?
Differentiate between Stack and Heap memory.
Explain the role of the Garbage Collector.
What is CLR? Mention its functions.
What is the Framework Class Library (FCL)?
What is .NET Standard 2.0?
List the applications of the .NET Framework.

Long Questions (10 Marks)

Explain the architecture of the .NET Framework with a neat diagram.
Describe the execution process of a C# program from source code to machine code.
Compare .NET Framework, .NET Core, Mono, Xamarin, and .NET MAUI.
Explain CLR and its services in detail.
Discuss the major components and applied technologies of the .NET Framework.

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