Learn Dot Net

Introduction to .NET

.NET is a free, open-source, cross-platform framework developed by Microsoft for building applications. It supports multiple programming languages like C#, VB.NET, and F#. The framework provides a unified environment for creating a wide range of applications, such as:

• Desktop Applications using Windows Forms or WPF.
• Web Applications using ASP.NET Core.
• Mobile Applications using Xamarin.
• Cloud Services using Azure.

Key Components:

1. Common Language Runtime (CLR): Manages code execution, memory, and garbage collection.
2. Base Class Library (BCL): A collection of reusable classes, interfaces, and value types.
3. .NET SDK: A set of tools and libraries to build applications.

Hands-on Demo

Scenario: Create a simple console application to demonstrate .NET basics.

1. Install .NET SDK from dotnet.microsoft.com.

2. Create a new project:

   dotnet new console -n HelloWorldApp
   cd HelloWorldApp
   dotnet run

3. Modify the Program.cs:

   Console.WriteLine("Hello, .NET World!");

4. Execute it using:

   dotnet run

Looping Control Structure

Types of Loops:

1. For Loop:

   for (int i = 0; i < 5; i++)
   {
       Console.WriteLine($"Iteration {i}");
   }

2. While Loop:

   int i = 0;
   while (i < 5)
   {
       Console.WriteLine($"Iteration {i}");
       i++;
   }

3. Do-While Loop:

   int i = 0;
   do
   {
       Console.WriteLine($"Iteration {i}");
       i++;
   } while (i < 5);

4. Foreach Loop:

   string[] fruits = { "Apple", "Banana", "Cherry" };
   foreach (var fruit in fruits)
   {
       Console.WriteLine(fruit);
   }

Boxing and Unboxing

• Boxing: Converting a value type to a reference type.

  int num = 10;
  object obj = num;  // Boxing

• Unboxing: Extracting a value type from an object.

  int unboxedNum = (int)obj;  // Unboxing

Method Overloading

Defining multiple methods with the same name but different parameters.

class Calculator
{
    public int Add(int a, int b) => a + b;
    public double Add(double a, double b) => a + b;
}

Constructors

A constructor initializes an object of a class.

class Person
{
    public string Name { get; }
    public Person(string name) { Name = name; }
}

Static Methods

Static methods belong to the class, not an instance.

class MathUtil
{
    public static int Square(int num) => num * num;
}

Inheritance

Derived classes inherit members of the base class.

class Animal { public void Eat() => Console.WriteLine("Eating"); }
class Dog : Animal { public void Bark() => Console.WriteLine("Barking"); }

Polymorphism

1. Compile-time Polymorphism (Method Overloading).

2. Runtime Polymorphism (Method Overriding).

   class Parent { public virtual void Speak() => Console.WriteLine("Parent speaks."); }
   class Child : Parent { public override void Speak() => Console.WriteLine("Child speaks."); }

String vs StringBuilder

1. String: Immutable.

   string str = "Hello";
   str += " World";  // New string is created.

2. StringBuilder: Mutable.

   StringBuilder sb = new StringBuilder("Hello");
   sb.Append(" World");  // Modifies the existing object.

Exception Handling

Handle runtime errors using try-catch-finally.

try
{
    int result = 10 / 0;
}
catch (DivideByZeroException ex)
{
    Console.WriteLine(ex.Message);
}
finally
{
    Console.WriteLine("Execution finished.");
}

Abstract Class

An abstract class provides a blueprint for derived classes.

abstract class Shape
{
    public abstract double CalculateArea();
}
class Circle : Shape
{
    public double Radius { get; set; }
    public override double CalculateArea() => Math.PI * Radius * Radius;
}

Connected Architecture and SQL Command

Connected architecture communicates directly with the database using SqlConnection and SqlCommand.

using System.Data.SqlClient;

string connectionString = "your_connection_string";
using (SqlConnection connection = new SqlConnection(connectionString))
{
    connection.Open();
    SqlCommand command = new SqlCommand("SELECT * FROM Users", connection);
    SqlDataReader reader = command.ExecuteReader();
    while (reader.Read())
    {
        Console.WriteLine(reader["Username"]);
    }
}

LINQ and Lambda Expressions

LINQ (Language-Integrated Query):

int[] numbers = { 1, 2, 3, 4, 5 };
var evenNumbers = numbers.Where(n => n % 2 == 0);

Lambda Expressions:

Func<int, int> square = x => x * x;
Console.WriteLine(square(5));  // Output: 25