C# Programming Course

Welcome to the C# Programming course on TechLearningPRO — a structured path from your first Hello World to production-ready ASP.NET Core APIs, Entity Framework Core, and intervi…

Before writing production C#, you need a reliable toolchain: the .NET SDK, an editor, and the C# Dev Kit extensions that power IntelliSense, debugging, and test discovery.

Every C# journey starts with a small program that compiles, runs, and prints output.

Variables store state in memory.

Operators transform values: arithmetic for calculations, comparison for branching, logical for compound conditions, and assignment for state updates.

Console I/O is the fastest way to prototype logic; production systems use structured logging, HTTP, and message buses.

if, else if, and else branch execution based on boolean conditions.

C# 8+ switch expressions replace verbose switch statements with concise, expression-oriented syntax that returns a value.

Loops repeat work: for with counters, foreach over collections, while for unknown iterations, and do-while for at-least-once execution.

break exits the nearest loop or switch; continue skips to the next iteration.

Pattern matching unifies type tests, deconstruction, and conditional logic into one expressive feature set.

Methods encapsulate behavior — parameters in, return values out, optional ref/out/in modifiers for advanced scenarios.

Overloading defines multiple methods with the same name but different parameter lists — count, types, or ref kinds.

Classes define blueprints; objects are runtime instances with fields, properties, and methods.

Constructors initialize object state at creation.

Encapsulation hides internal state behind controlled interfaces — private fields, public properties with validation, and methods that enforce invariants.

Inheritance models is-a relationships: SavingsAccount is an Account.

Polymorphism lets code treat different types uniformly through a common base or interface — runtime dispatch calls the correct override.

Abstraction hides complexity behind simplified models — you call TransferMoney without knowing ledger SQL details.

Interfaces define contracts — method signatures without implementation (until default interface methods).

Arrays are fixed-length, zero-indexed contiguous collections — T[].

List<T> is the default mutable collection — dynamic array backing with amortized O(1) Add.

Dictionary<TKey,TValue> provides O(1) average hash-based lookups — essential for caches, indexes, and grouping.

HashSet<T> stores unique elements with O(1) Contains — ideal for deduplication, visited tracking, and set algebra (Union, Intersect, Except).

Queue<T> is FIFO (first in, first out); Stack<T> is LIFO (last in, first out).

LINQ (Language Integrated Query) queries collections declaratively with Where, Select, OrderBy, GroupBy — unified syntax for IEnumerable and IQueryable.

Advanced LINQ covers GroupBy aggregations, Join relational-style merges, Aggregate folds, Zip, set operators, and custom operators.

Exceptions signal exceptional failure — not normal control flow.

Custom exceptions express domain failures — InsufficientFundsException, PatientNotFoundException — enabling callers to catch precisely without string matching.

File APIs span System.IO — File, Directory, FileStream, StreamReader/Writer, and async variants.

Serialization converts objects to storable/transmittable formats — binary, XML, JSON.

JSON dominates web APIs.

A delegate is a type-safe function pointer — references methods matching a signature.

Events wrap delegates with publish-subscribe semantics — only the declaring class can raise (invoke) them; external code subscribes with +=.

Lambdas are inline anonymous functions — (x, y) => x + y — powering LINQ, Task.Run, and fluent configuration.

Generics parameterize types — List<T>, Dictionary<TKey,TValue>, your own Repository<TEntity> — providing compile-time type safety without boxing value types.

Extension methods add methods to existing types without modification — static methods in static classes with first parameter marked this.

async/await models asynchronous I/O without blocking threads — critical for ASP.NET Core scalability.

Dependency Injection in ASP.NET Core registers services in Program.cs and resolves them via constructor injection.

ASP.NET Core builds REST APIs with minimal APIs or controllers, model binding, validation, OpenAPI/Swagger, and ProblemDetails error responses.

Entity Framework Core is the ORM mapping C# classes to relational tables — LINQ queries translate to SQL.

ILogger<T> structured logging integrates Console, Debug, EventSource, and third-party sinks (Serilog, Application Insights).

xUnit is the dominant .NET test framework — [Fact] for single tests, [Theory] with [InlineData] for parameterized cases.

.NET 8 delivers impressive throughput, but performance still requires discipline: avoid allocations in hot paths, use Span<T>, pool objects, cache wisely, and profile befo…

You have covered C# syntax, OOP, collections, LINQ, async, DI, EF Core, APIs, logging, testing, and performance. Includes interactive C# interview question bank.