C# Basics

C# = modern, object-oriented language for .NET

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What is C#?

"Microsoft's object-oriented language"

C# is a modern, object-oriented programming language developed by Microsoft for the .NET platform.

"C# is a modern, strongly-typed, object-oriented programming language developed by Microsoft, primarily used for building .NET applications."

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Key Characteristics

Object-oriented · Strongly typed · Garbage collected

• Object-oriented: Classes, inheritance, polymorphism
• Strongly typed: Type safety at compile time
• Garbage collected: Automatic memory management
• Modern features: LINQ, async/await, generics

"C# is object-oriented, strongly-typed, garbage-collected, and includes modern features like LINQ and async/await."

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Data Types

Value types · Reference types

Value types (stack):

• int, double, bool, char
• struct, enum

Reference types (heap):

• class, interface, delegate
• string, array, object

"C# has value types (stored on stack) and reference types (stored on heap), with different memory behavior."

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Classes and Objects

Class = blueprint, Object = instance

class Person
{
    public string Name { get; set; }
    public int Age { get; set; }

    public void Greet()
    {
        Console.WriteLine($"Hello, {Name}");
    }
}

Person person = new Person();
person.Name = "John";

"Classes define blueprints for objects, which are instances created with the 'new' keyword."

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Properties

Auto-properties · Get/Set

// Auto-property
public string Name { get; set; }

// With backing field
private string _name;
public string Name
{
    get { return _name; }
    set { _name = value; }
}

// Read-only
public int Id { get; }

"Properties provide controlled access to class fields, with auto-properties, get/set accessors, and read-only options."

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Methods

Return type · Parameters · Overloading

// Method
public int Add(int a, int b)
{
    return a + b;
}

// Method overloading
public int Add(int a, int b, int c)
{
    return a + b + c;
}

// Void method
public void Print(string message)
{
    Console.WriteLine(message);
}

"Methods define behavior, support overloading (same name, different parameters), and can return values or be void."

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Inheritance

Base class · Derived class

class Animal
{
    public virtual void MakeSound()
    {
        Console.WriteLine("Sound");
    }
}

class Dog : Animal
{
    public override void MakeSound()
    {
        Console.WriteLine("Woof");
    }
}

"Inheritance allows classes to inherit from base classes, with virtual/override for polymorphism."

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Interfaces

Contract without implementation

interface IShape
{
    double CalculateArea();
}

class Circle : IShape
{
    public double CalculateArea()
    {
        return Math.PI * radius * radius;
    }
}

"Interfaces define contracts that classes implement, enabling polymorphism and loose coupling."

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9️⃣ Generics

Type parameters for reusability

class List<T&gt
{
    private T[] items;
    public void Add(T item) { }
}

List<int> numbers = new List<int>();
List<string> names = new List<string>();

"Generics enable type-safe, reusable code by using type parameters instead of specific types."

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LINQ

Language Integrated Query

var numbers = new[] { 1, 2, 3, 4, 5 };
var evens = numbers.Where(n => n % 2 == 0);
var sum = numbers.Sum();

"LINQ provides query capabilities integrated into C#, enabling powerful data manipulation with a SQL-like syntax."

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Async/Await

Asynchronous programming

async Task<string> FetchDataAsync()
{
    var data = await httpClient.GetStringAsync(url);
    return data;
}

"Async/await enables asynchronous programming, allowing non-blocking I/O operations and better performance."

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Exception Handling

try · catch · finally

try
{
    // Code that might throw
}
catch (Exception ex)
{
    // Handle exception
}
finally
{
    // Always executes
}

"Exception handling uses try/catch/finally blocks to handle errors gracefully and ensure cleanup."

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"C# is a modern, object-oriented, strongly-typed language for .NET. It supports value and reference types, classes with inheritance, interfaces for contracts, generics for reusability, LINQ for queries, and async/await for asynchronous programming. C# is garbage-collected and provides exception handling with try/catch/finally."

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🧠 Ultra-Short Cheat Sheet

Object-oriented
Strongly typed
Value types vs Reference types
Classes, inheritance, interfaces
Properties, methods
Generics
LINQ
Async/await
Exception handling