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C# and .NET flashcards

Microsoft's typed language and platform for web APIs, business apps, games and cloud services.

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Beginner friendly, starts from zero
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C# and .NETStart from zero · 1 of 11

What is C#, in one plain sentence?

C# (said "see sharp") is a programming language made by Microsoft for writing apps: websites, phone apps, games, office tools and the programs that run behind them.

C# is the language; .NET is the toolbox it works with.
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All topics

What you will learn

  1. Start from zero

    • What C# and .NET are5 cards
    • First words and first program6 cards

  2. Core basics

    • Values, types and strings4 cards
    • Decisions, loops and methods3 cards
    • Classes, records and interfaces5 cards
    • Collections, null safety and errors3 cards
    • Project tools and packages2 cards

  3. Next steps

    • LINQ, async and patterns6 cards
    • Web APIs with ASP.NET Core5 cards
    • Data with EF Core4 cards
    • Testing and logging2 cards

  4. Go deeper

    • Memory and runtime internals5 cards
    • Modern C# 14 and .NET 103 cards
    • Async internals2 cards
    • Security and data safety4 cards
    • Performance and deployment3 cards

Final test and certificate

10 questions drawn fresh from the whole topic, about 15 minutes. Sign in, score 80% or more and get a free certificate with your name and a public check link anyone can open, such as an employer or a teacher. Not signed in? Try a practice test from the cards.

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About these cards

  • Reviewed 26 October 2026
  • Covers.NET 10 (LTS)C# 14ASP.NET Core 10EF Core 10
How these cards are made

C# and .NET at a glance

C# is a language for building apps, and .NET is the free platform that runs them on Windows, Mac and Linux.

C# is the recipe you write; .NET is the kitchen with ovens, knives and a pantry ready to use.

Words you will meet

Variable
A named box that holds a value you can read and change
Type
What kind of value something is, like a whole number or text
Method
A named set of steps the program can run
Class
A design that groups data and methods together
Object
One real copy made from a class
Compiler
The tool that checks your code and turns it into something .NET can run
SDK
The free kit you install to build and run .NET apps

The steps

  1. 1. Start from zero (11 cards): What C# and .NET are, where they are used, and the words you need for your first program.
  2. 2. Core basics (17 cards): Types, strings, decisions, loops, methods, classes, records, collections, null safety and the dotnet tools.
  3. 3. Next steps (17 cards): LINQ, async, web APIs, dependency injection, settings, EF Core, testing and logging.
  4. 4. Go deeper (17 cards): Memory, spans, C# 14, async internals, concurrency, security, profiling and Native AOT.
All 11 cards in Start from zero
What is C#, in one plain sentence?
C# (said "see sharp") is a programming language made by Microsoft for writing apps: websites, phone apps, games, office tools and the programs that run behind them.
What is .NET, and how is it different from C#?
C# is the language you write. .NET is the free platform that runs your program and gives it ready-made parts, like reading files, talking to the internet and saving data.
Where do you meet C# and .NET in daily life without knowing it?
Bank and insurance websites, office tools at work, many games built with the Unity engine, and the servers behind shopping and booking apps often run C#.
What is a program, in the simplest words?
A program is a list of exact steps for a computer, written in a language it can follow. The computer does the steps in order, very fast, and never guesses what you meant.
Give an everyday picture of how a C# program gets run.
You write text in a file, a tool called the compiler checks it and turns it into a form .NET understands, then .NET runs it. If the compiler finds a mistake, it tells you before anything runs.
What does this tiny program do?
It prints the words Hello, Arjun! on the screen. Console.WriteLine means "write a line of text to the window". The words in quotes are the text.
Key word: what is a variable?
A variable is a named box that holds a value, like age holding 30. You can read it later and change what is inside. In C# each box also says what kind of value it holds.
Key word: what is a type?
A type says what kind of value something is: a whole number (int), text (string), yes or no (bool) or a price with decimals (decimal). C# checks types so you cannot add a name to a number by mistake.
Key words: what are a method, a class and an object?
A method is a named set of steps, like "send invoice". A class is a design that groups data and methods, like a form for a customer. An object is one filled-in copy of that design, like customer Rahul.
What do you need to start writing C#?
A computer (Windows, Mac or Linux), the free .NET SDK from Microsoft, and a code editor such as Visual Studio or VS Code. Then the command dotnet new console makes your first project.
What will you be able to do after this topic?
Write C# programs that make decisions, store lists of data, read and save files, build a small web API, talk to a database with EF Core, and test your code. The later levels add speed, safety and good design.
C# and .NET cheatsheet

dotnet CLI

  • dotnet new console -o App New console project
  • dotnet new webapi -o Api New web API project
  • dotnet run Build and run
  • dotnet test Run all tests
  • dotnet add package Name Add a NuGet package
  • dotnet publish -c Release Build for deployment
  • dotnet run app.cs Run a single file (.NET 10)

Syntax

  • var x = 5; Inferred, still typed
  • $"Hi {name}" Interpolated string
  • x ?? fallback Use fallback when null
  • obj?.Prop Null-safe access
  • record Money(decimal A); Value-equal data type
  • x switch { 1 => "a", _ => "b" } Switch expression

LINQ

  • Where(x => ...) Filter
  • Select(x => ...) Shape each item
  • OrderBy / ThenBy Sort
  • GroupBy(x => x.Key) Group
  • Any() / All() Test a condition
  • ToList() / ToListAsync() Run the query now

ASP.NET Core

  • app.MapGet("/x", ...) GET endpoint
  • builder.Services.AddScoped<I, T>() Register per request
  • Results.NotFound() Return 404
  • RequireAuthorization("Policy") Protect endpoint
  • builder.Configuration["Key"] Read a setting

EF Core

  • dotnet ef migrations add Name New migration
  • dotnet ef database update Apply migrations
  • Include(o => o.Customer) Load related data
  • AsNoTracking() Read-only, faster
  • SaveChangesAsync() Write changes
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