C# Basics: Lists and Collections Explained

As your programs grow in complexity, you’ll often need to store and manage multiple values — not just one. Instead of creating dozens of variables, C# gives you powerful tools like lists and collections that make it easy to group and manipulate data.

This is where we’ll cover the most common and useful collections in C#, focusing on arrays, List, and briefly introducing other collections. You’ll learn how to store, access, loop through, and modify items in a way that’s efficient and easy to read.

🧺 What Is a Collection?

A collection is a container that holds multiple items (like numbers, names, or objects). Collections help you:

• Store and group related data
• Loop through multiple values
• Add, remove, or update items dynamically

🔢 Arrays (Fixed-Size Collection)

An array holds a fixed number of items of the same type.

🔸 Declaring an Array

int[] numbers = new int[3];
numbers[0] = 10;
numbers[1] = 20;
numbers[2] = 30;

🔹 Or declare and assign in one step:

string[] fruits = { "Apple", "Banana", "Cherry" };

🔁 Looping Through an Array:

foreach (string fruit in fruits)
{
    Console.WriteLine(fruit);
}

🚨 Arrays are fixed in size — once declared, they can’t grow or shrink.

📋 Lists (Flexible and Dynamic)

A List<T> is a generic collection that can grow and shrink. It’s more powerful and flexible than arrays.

🔸 Add the namespace:

using System.Collections.Generic;

🔸 Create and use a list:

List<string> colours = new List<string>();

colours.Add("Red");
colours.Add("Green");
colours.Add("Blue");

foreach (string colour in colours)
{
    Console.WriteLine(colour);
}

🔹 Other common List operations:

colours.Remove("Green");          // Removes the item
bool hasRed = colours.Contains("Red"); // Checks for existence
int count = colours.Count;        // Number of items
colours.Clear();                  // Removes all items

🧪 Example: Working with Numbers in a List

List<int> scores = new List<int> { 85, 92, 78, 96 };

int total = 0;
foreach (int score in scores)
{
    total += score;
}
double average = (double)total / scores.Count;

Console.WriteLine("Average Score: " + average);

📦 Array vs List – When to Use

🔁 Bonus: Other Useful Collections

As you grow in C#, explore:

• Dictionary<TKey, TValue> — key-value pairs
• HashSet<T> — unique items only
• Queue<T> and Stack<T> — FIFO and LIFO structures

But for now, mastering arrays and lists will cover 90% of what you need in early-stage development.

🧠 Practice Task

Write a program that:

• Stores 5 names in a List<string>
• Asks the user to enter a name
• Checks whether it exists in the list and prints an appropriate message

List<string> names = new List<string> { "Alice", "Bob", "Charlie", "Dana", "Eva" };

Console.Write("Enter a name: ");
string input = Console.ReadLine();

if (names.Contains(input))
{
    Console.WriteLine($"{input} is in the list.");
}
else
{
    Console.WriteLine($"{input} is not found.");
}

📚 Summary

📬 Need help choosing the right collection for your project, or want guidance with collection-based challenges? Reach out to us via our Contact Page — we’re here to support your learning with code help, worksheets, or project advice.