অ্যারেস এবং লিস্টস (Arrays & Lists)

// Create an array with initial values
string[] planets = { "Mercury", "Venus", "Earth", "Mars" };

// Access by index (0-based!)
Console.WriteLine($"First planet:  {planets[0]}");
Console.WriteLine($"Third planet:  {planets[2]}");
Console.WriteLine($"Total planets: {planets.Length}");

// Modify an element
planets[3] = "Red Planet";
Console.WriteLine($"Mars is now:   {planets[3]}");

// Create an empty array of size 5
int[] scores = new int[5]; // all zeros by default
scores[0] = 95;
scores[1] = 87;

// Loop through with foreach
Console.Write("Scores: ");
foreach (int s in scores)
    Console.Write($"{s} ");
Console.WriteLine();

// Loop with index using for
for (int i = 0; i < planets.Length; i++)
    Console.WriteLine($"  [{i}] {planets[i]}");

First planet:  Mercury
Third planet:  Earth
Total planets: 4
Mars is now:   Red Planet
Scores: 95 87 0 0 0 
  [0] Mercury
  [1] Venus
  [2] Earth
  [3] Red Planet

// Create a list
List<string> snacks = new List<string> { "Chips", "Cookies", "Popcorn" };

// Add items
snacks.Add("Pretzels");
snacks.Add("Candy");
Console.WriteLine($"Snacks: {snacks.Count}"); // Count, not Length!

// Insert at a specific position
snacks.Insert(0, "Fruit"); // add at the beginning

// Remove items
snacks.Remove("Candy");     // remove by value
snacks.RemoveAt(2);         // remove by index

// Check if item exists
Console.WriteLine($"Has Chips? {snacks.Contains("Chips")}");

// Print all snacks
foreach (string snack in snacks)
    Console.WriteLine($"  - {snack}");

// Sort alphabetically
snacks.Sort();
Console.WriteLine("\nSorted:");
foreach (string snack in snacks)
    Console.WriteLine($"  - {snack}");

Snacks: 5
Has Chips? True
  - Fruit
  - Chips
  - Popcorn
  - Pretzels

Sorted:
  - Chips
  - Fruit
  - Popcorn
  - Pretzels

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

// Where — filter items
var evens = numbers.Where(n => n % 2 == 0);
Console.Write("Evens: ");
foreach (int n in evens) Console.Write($"{n} ");
Console.WriteLine();

// Select — transform items
var doubled = numbers.Select(n => n * 2);
Console.Write("Doubled: ");
foreach (int n in doubled) Console.Write($"{n} ");
Console.WriteLine();

// Chain them together!
var bigEvensDoubled = numbers
    .Where(n => n % 2 == 0)
    .Where(n => n > 4)
    .Select(n => n * 2);
Console.Write("Big evens doubled: ");
foreach (int n in bigEvensDoubled) Console.Write($"{n} ");
Console.WriteLine();

// Convert LINQ result to List
List<int> result = numbers.Where(n => n > 7).ToList();
Console.WriteLine($"Numbers > 7: [{string.Join(", ", result)}]");

Evens: 2 4 6 8 10 
Doubled: 2 4 6 8 10 12 14 16 18 20 
Big evens doubled: 12 16 20 
Numbers > 7: [8, 9, 10]