Dasar

Hello World

Console.WriteLine("Hello, World!");  // top-level (C# 10+)
// Classic: class Program { static void Main() { ... } }

Build & Jalankan

dotnet new console -n MyApp   # create project
dotnet run                     # compile and run
dotnet build                   # compile only

Variabel & Konstanta

int x = 42;
var name = "Alice";           // type inference
const double Pi = 3.14159;
readonly int maxRetries = 3;  // set once, in ctor

Tipe

Value Type

int	Integer 32-bit bertanda
long	Integer 64-bit bertanda
float	Floating point 32-bit (suffix `f`)
double	Floating point 64-bit
decimal	Presisi tinggi 128-bit (suffix `m`)
bool	`true` / `false`
char	Karakter Unicode 16-bit

Reference Type

string	Teks UTF-16 yang immutable
object	Tipe dasar semua tipe
dynamic	Lewati pemeriksaan tipe compile-time
int[]	Array integer
List<T>	Daftar generik (System.Collections.Generic)

Nullable & Tuple

int? age = null;               // nullable value type
string? name = null;           // nullable reference (C# 8+)
var point = (X: 1, Y: 2);     // named tuple
Console.WriteLine(point.X);

Fitur String

string name = "World";
string msg = $"Hello, {name}!";       // interpolation
string path = @"C:\Users\file.txt";   // verbatim
string raw = """raw "string" here""";  // raw (C# 11+)

Control Flow

If / Else

if (x > 0) Console.WriteLine("positive");
else if (x == 0) Console.WriteLine("zero");
else Console.WriteLine("negative");

Switch & Pattern Matching

string label = x switch {
    > 0 => "positive", 0 => "zero", _ => "negative"
};
if (obj is string s && s.Length > 0) { }  // pattern match

Loop

for (int i = 0; i < 10; i++) { }
foreach (var item in collection) { }
while (condition) { }
do { } while (condition);

Class

Definisi Class

public class Person {
    public string Name { get; set; }
    public int Age { get; init; }       // init-only (C# 9+)
    public Person(string name, int age) { Name = name; Age = age; }
}

Record (C# 9+)

public record Point(double X, double Y);
var p1 = new Point(1, 2);
var p2 = p1 with { X = 3 };  // non-destructive copy
// auto: Equals, GetHashCode, ToString, deconstruct

Inheritance

public abstract class Shape { public abstract double Area(); }
public class Circle(double r) : Shape {
    public override double Area() => Math.PI * r * r;
}

Access Modifier

public	Dapat diakses dari mana saja
private	Hanya class yang sama (default untuk member)
protected	Class yang sama dan class turunan
internal	Hanya assembly yang sama (default untuk class)
protected internal	Assembly yang sama atau class turunan

Interface

Definisi Interface

public interface IShape {
    double Area();
    double Perimeter() => 0;  // default impl (C# 8+)
}
public class Rect(double w, double h) : IShape { public double Area() => w * h; }

Interface Umum

IEnumerable<T>	Dukungan iterasi (foreach, LINQ)
IDisposable	Pembersihan deterministik (pernyataan `using`)
IComparable<T>	Pengurutan alami untuk sorting
IEquatable<T>	Perbandingan kesetaraan nilai
ICloneable	Kloning objek

LINQ

Sintaks Method

var result = numbers
    .Where(n => n > 3)
    .OrderBy(n => n)
    .Select(n => n * 2)
    .ToList();

Sintaks Query

var result = from n in numbers
             where n > 3
             orderby n
             select n * 2;

Method LINQ Umum

.Where(pred)	Filter elemen
.Select(func)	Proyeksi / transformasi elemen
.OrderBy(key)	Urutkan ascending
.GroupBy(key)	Kelompokkan elemen berdasarkan key
.First() / .FirstOrDefault()	Elemen pertama (atau default)
.Any(pred)	`true` jika ada elemen yang cocok
.Count()	Jumlah elemen
.Sum() / .Average()	Agregasi nilai numerik
.Distinct()	Hapus duplikat
.SelectMany(func)	Ratakan koleksi bersarang

Async/Await

Method Async

public async Task FetchAsync(string url) {
    using var client = new HttpClient();
    return await client.GetStringAsync(url);
}

Kombinator Task

var results = await Task.WhenAll(task1, task2, task3);
var first = await Task.WhenAny(task1, task2);

Pola Async

Task	Return async void (tanpa hasil)
Task<T>	Return async dengan hasil bertipe T
ValueTask<T>	Task ringan untuk jalur sync-fast
await foreach	Iterasi async atas `IAsyncEnumerable`
CancellationToken	Pembatalan kooperatif untuk operasi async

Koleksi

Koleksi Umum

List<T>	Array dinamis, akses indeks cepat
Dictionary<K,V>	Hash map, lookup O(1) berdasarkan key
HashSet<T>	Elemen unik, lookup O(1)
Queue<T>	Koleksi FIFO
Stack<T>	Koleksi LIFO
LinkedList<T>	Linked list dua arah
SortedDictionary<K,V>	Diurutkan berdasarkan key (berbasis tree)

Penggunaan Dictionary

var dict = new Dictionary {
    ["Alice"] = 90, ["Bob"] = 85
};
dict.TryGetValue("Alice", out int score);
foreach (var (key, val) in dict) { }

Koleksi Immutable

using System.Collections.Immutable;
var list = ImmutableList.Create(1, 2, 3);
var newList = list.Add(4);  // returns new list

Property

Sintaks Property

public string Name { get; set; }
public int Age { get; private set; }
public string Email { get; init; }        // init-only
public string Display => $"{Name} ({Age})"; // computed

Indexer

public double this[int row, int col] {
    get => data[row, col];
    set => data[row, col] = value;
}

Pola Property

{ get; set; }	Auto-property read-write
{ get; }	Read-only (hanya bisa di-set dalam constructor)
{ get; init; }	Read-only setelah inisialisasi (C# 9+)
{ get; private set; }	Bisa dibaca publik, ditulis privat
=> expression	Property expression-bodied (computed)

Exception

Try / Catch / Finally

try { int result = int.Parse(input); }
catch (FormatException ex) { Console.Error.WriteLine(ex.Message); }
catch (Exception ex) when (ex is not OutOfMemoryException) { }
finally { /* always executes */ }

Pernyataan Using

using var file = File.OpenRead("data.txt");
// file.Dispose() called automatically at scope end
// equivalent to try/finally with Dispose()

Exception Umum

ArgumentNullException	Argumen null dikirim ke method
ArgumentOutOfRangeException	Argumen di luar rentang valid
InvalidOperationException	Operasi tidak valid untuk kondisi saat ini
NullReferenceException	Dereference objek null
KeyNotFoundException	Key tidak ditemukan dalam dictionary
NotImplementedException	Method belum diimplementasikan

Exception Kustom

public class AppException : Exception {
    public int Code { get; }
    public AppException(string msg, int code)
        : base(msg) { Code = code; }
}

REFERENSI CEPAT C#