C# Collections

List, Dictionary and HashSet.

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System.Collections.Generic provides type-safe collections:

List<T>: Add(), Remove(), Count, Sort(), Contains()
Dictionary<TKey, TValue>: key → value; TryGetValue(), ContainsKey()
HashSet<T>: unique values
Queue<T> and Stack<T>

Key Takeaways: C# Collections

Mastering C# Collections helps you write clean and reliable C# code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

C# Collections Code Example

var cities = new List<string> { "Lahore", "Karachi" };
cities.Add("Quetta");
cities.Remove("Karachi");
cities.Sort();
Console.WriteLine(string.Join(", ", cities) + $" ({cities.Count})");

var stock = new Dictionary<string, int> { ["Laptop"] = 12, ["Mouse"] = 150 };
stock["Monitor"] = 25;
if (stock.TryGetValue("Mouse", out int qty)) Console.WriteLine($"Mouse: {qty}");

var tags = new HashSet<string> { "csharp", "dotnet", "csharp" };
Console.WriteLine(tags.Count);

Output