Collections & Generics

🔷 C# Programming Lesson 12 Advanced

Unlike raw fixed arrays, C# generic collections dynamically resize automatically and provide type safety, avoiding expensive boxing/unboxing overhead.

1 Collection Architecture: List, Dictionary, and HashSet

Common generic containers in the `System.Collections.Generic` namespace include:

List<T>: A dynamic, ordered list of items.
Dictionary<TKey, TValue>: Stores unique key-value pairs for quick lookups.
HashSet<T>: An unordered collection containing only unique elements.

2 Collections Code

Let's run a program performing list inserts, unique set operations, and key-value lookups:

C# — Generic Collections ▶ Run Code

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        // 1. List
        List<string> list = new List<string>() { "Apple", "Banana" };
        list.Add("Apple"); // Duplicates allowed
        Console.WriteLine("List count: " + list.Count);

        // 2. HashSet
        HashSet<string> set = new HashSet<string>() { "Apple", "Banana" };
        set.Add("Apple"); // Duplicate ignored
        Console.WriteLine("HashSet count: " + set.Count);

        // 3. Dictionary (Key-Value)
        Dictionary<string, int> map = new Dictionary<string, int>();
        map["Alice"] = 95;
        map["Bob"] = 88;
        Console.WriteLine("Bob's score: " + map["Bob"]);
    }
}

3 Code Challenge

Challenge: Write a program that instantiates a `List`, adds 5 values, removes the value at index 2, and prints the remaining items. Create a `Dictionary` mapping products to prices and print the price values.