Collections and LINQ

C# provides a rich set of collection types and LINQ (Language Integrated Query) for querying and transforming data. Together, they form one of the most powerful features of the language.

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Common Collection Types

Arrays

Fixed-size, strongly typed collections:

int[] numbers = { 1, 2, 3, 4, 5 };
string[] names = new string[3];
names[0] = "Alice";

// Multi-dimensional
int[,] matrix = { { 1, 2 }, { 3, 4 } };

// Jagged (array of arrays)
int[][] jagged = new int[3][];
jagged[0] = new[] { 1, 2, 3 };

List

A resizable, generic collection (the most commonly used):

var fruits = new List<string> { "Apple", "Banana", "Cherry" };
fruits.Add("Date");
fruits.Remove("Banana");
fruits.Insert(1, "Blueberry");

Console.WriteLine(fruits.Count);       // 3
Console.WriteLine(fruits.Contains("Apple")); // true

Dictionary<TKey, TValue>

Key-value pairs with fast lookup:

var capitals = new Dictionary<string, string>
{
    ["UK"] = "London",
    ["France"] = "Paris",
    ["Germany"] = "Berlin"
};

// Safe lookup
if (capitals.TryGetValue("UK", out string? capital))
{
    Console.WriteLine(capital); // London
}

Other Collections