01. Getting Started with C#

What you'll learn

• 1Understand what .NET 8 LTS means and the difference between SDK and Runtime
• 2Pick one of the IDEs (Visual Studio / VS Code / Rider) and install it
• 3Create your first project with `dotnet new console`
• 4Run it with `dotnet run` and check the output
• 5Do simple I/O with `Console.WriteLine` / `Console.ReadLine`

Overview

C# is a statically-typed language built by Microsoft, used everywhere from games (Unity) and web (ASP.NET) to desktop and mobile. In this lecture you'll install the .NET 8 SDK, create a console project, and run it yourself.

Core Concepts

1) What is .NET?

**.NET** is the runtime + standard library + SDK bundle that runs languages like C#, F#, and VB.NET. Code you write once can run on Windows, macOS, and Linux.

• **.NET 8 LTS**: the Long Term Support release published in November 2023. Officially supported until November 2026.
• **SDK**: the compiler and tool set needed for development (includes the `dotnet` CLI)
• **Runtime**: the minimum components needed just to run a built program

2) Verifying the SDK install

After installing, run the following in a terminal.

dotnet --version
# example output: 8.0.xxx

If it starts with `8.0`, you're good. If the command isn't found, grab the **.NET 8 SDK** from [https://dotnet.microsoft.com/download](https://dotnet.microsoft.com/download).

3) Choosing an IDE

• **Visual Studio 2022 (Windows)** — heavy but the most integrated experience
• **VS Code + C# Dev Kit (cross-platform)** — light and fast, recommended
• **JetBrains Rider** — paid but with great refactoring

This course is IDE-agnostic. Whichever you pick, behavior via the `dotnet` CLI is identical.

4) Creating your first project

dotnet new console -o HelloApp
cd HelloApp
dotnet run

• `dotnet new console`: creates a console-app template
• `-o HelloApp`: generates it inside a `HelloApp` folder
• `dotnet run`: builds (auto-`restore` if needed) → runs

On the first run, it prints `Hello, World!`.

5) Top-level statements

Since .NET 6 you can skip the `Main` method and write code directly.

// Program.cs
Console.WriteLine("Hello!");

`Console.WriteLine` prints with a trailing newline, `Console.Write` prints without one.

Examples

Example 1 — `HelloApp/Program.cs`: the most basic

// Your first C# program
Console.WriteLine("Hello, C# !");

**Output**

Hello, C# !

**Note:** Don't forget the semicolon (`;`). C# delimits statements with `;`, not newlines.

Example 2 — `Echo/Program.cs`: take input and greet

Console.Write("Enter your name: ");
string? name = Console.ReadLine();
Console.WriteLine($"Hello, {name}!");

**Output**

Enter your name: Alex
Hello, Alex!

**Note:** `Console.ReadLine()` can return `null` if there is no input, so its type is `string?`. (More on this in lecture 2.)

Example 3 — `MultiPrint/Program.cs`: multiple lines + string interpolation

string product = "Apple";
int count = 3;
int price = 1500;

Console.WriteLine("=== Purchase summary ===");
Console.WriteLine($"Product: {product}");
Console.WriteLine($"Quantity: {count}");
Console.WriteLine($"Total: {count * price} won");

**Output**

=== Purchase summary ===
Product: Apple
Quantity: 3
Total: 4500 won

**Note:** The `{ }` inside `$"..."` can hold any expression. This is called **string interpolation**.

Full example code (src/)

src/Echo/Echo.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <RootNamespace>CodingNow.Lecture.Basics01</RootNamespace>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

src/Echo/Program.cs

// Greet the user by name
Console.Write("Enter your name: ");
string? name = Console.ReadLine();
Console.WriteLine($"Hello, {name}!");

src/HelloApp/HelloApp.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <RootNamespace>CodingNow.Lecture.Basics01</RootNamespace>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

src/HelloApp/Program.cs

// Your first C# program
Console.WriteLine("Hello, C# !");

src/MultiPrint/MultiPrint.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <RootNamespace>CodingNow.Lecture.Basics01</RootNamespace>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

src/MultiPrint/Program.cs

// Multiple lines + string interpolation
string product = "Apple";
int count = 3;
int price = 1500;

Console.WriteLine("=== Purchase summary ===");
Console.WriteLine($"Product: {product}");
Console.WriteLine($"Quantity: {count}");
Console.WriteLine($"Total: {count * price} won");

Common Mistakes

1. Writing `Console.Writeline` with the wrong casing — C# is **case-sensitive**.
2. Forgetting the trailing `;` — compile error.
3. Writing `"{name}"` without the `$` — the literal `{name}` is printed.
4. Running `dotnet run` outside the project folder and getting a "project not found" error.
5. Confusing `.NET Framework 4.x` with `.NET 8` — this course targets **.NET 8** (the Core line).

Summary

• Install the .NET 8 SDK and verify with `dotnet --version`
• The basic flow is `dotnet new console -o name` → `dotnet run`
• Use `Console.WriteLine` to output and `Console.ReadLine` to read input
• Use `$"..."` string interpolation to inject variables cleanly

Practice

**Practice - 01. Getting Started with C#**

Problem 1 — Self-introduction printer

• Project folder: `Homework01/`
• Key concepts: `Console.WriteLine`, string interpolation

Requirements

• Declare three variables: name, age, city
• Print in this format:

``` Hello! My name is OOO and I'm OO years old. I live in OO. ```

Expected output

Hello!
My name is Alex and I'm 25 years old.
I live in Seoul.

Hints

• Declare variables like `string name = "Alex";`
• Use string interpolation like `$"My name is {name}..."`

Problem 2 — Greet with current time

• Project folder: `Homework02/`
• Key concepts: `DateTime.Now`, string interpolation

Requirements

• Read the user's name
• Print the current time alongside the greeting (using `DateTime.Now`)

Expected output

Name: Min
Hello, Min!
The current time is 2025-05-18 14:30:00.

Hints

• Format time as `$"{DateTime.Now:yyyy-MM-dd HH:mm:ss}"`
• `Console.ReadLine()` returns `string?`

Check your answer

Try it yourself, then compare against the [`answer/`](./answer/) folder.

Answer (answer/)

homework/answer/Homework01/Homework01.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <RootNamespace>CodingNow.Lecture.Basics01</RootNamespace>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

homework/answer/Homework01/Program.cs

// Self-introduction printer
string name = "Alex";
int age = 25;
string city = "Seoul";

Console.WriteLine("Hello!");
Console.WriteLine($"My name is {name} and I'm {age} years old.");
Console.WriteLine($"I live in {city}.");

homework/answer/Homework02/Homework02.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <RootNamespace>CodingNow.Lecture.Basics01</RootNamespace>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

homework/answer/Homework02/Program.cs

// Greet with current time
Console.Write("Name: ");
string? name = Console.ReadLine();

Console.WriteLine($"Hello, {name}!");
Console.WriteLine($"The current time is {DateTime.Now:yyyy-MM-dd HH:mm:ss}.");

Try It Yourself

cd src/HelloApp
dotnet run

cd ../Echo
dotnet run

cd ../MultiPrint
dotnet run

Next Lecture

[02_Variables_and_Types](../02_%EB%B3%80%EC%88%98%EC%99%80_%ED%83%80%EC%9E%85/) — Learn the container for values: variables and types.