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C# Array vs List: Differences & Performance

May 2, 2022 | .NET, C#

When it comes to storing and manipulating data in C#, there are two main data structures you can use: arrays and lists. Both of these structures have their own unique benefits and drawbacks, and understanding when to use one over the other is key to writing efficient and effective code.

In this article, we will dive deep into the differences between arrays and lists in C#, discussing their performance, memory usage, and common use cases.

What is an Array in C#?

You always hear folks say – “Array, that’s basic stuff”. Sure it is, but how well acquainted are you with them? Let’s dive in, shall we?

An array in C# is somewhat like an arsenal of items, all of the same kind. Think of it like a row of lockers, each one numbered and each one housing an item. Ah, but there’s a catch. Once set up, you can’t add more lockers! Yep, that’s right, the size is immutable once defined.

Every item or ‘element’ as we usually call it, is identifiable by a unique index (hey, we gotta know where we kept what, right?). The counting starts from a big fat zero and goes upwards.

In the upcoming sections, we will unleash the magic behind creating arrays, storing elements in them, and accessing those same elements. Let’s have some fun!

How an Array works in C#?

Let’s dive right in and start creating arrays in C#. Like putting up a shelf for your books, but in the world of code.

Here’s an example of how you’d create an array that can store integers:

int[] arrayOInts = new int[5];

What are we doing here? We’re rolling out a fresh new int array named arrayOInts that can store 5 integer variables. Cool, huh?

Now, you’ve got this nice array, but how do you put stuff in it? Well, here’s how:

arrayOInts[0] = 10;  //Filling the first locker
arrayOInts[1] = 20;  //... and the second
arrayOInts[2] = 30;  //You get the idea
arrayOInts[3] = 40;  //Keep filling 
arrayOInts[4] = 50;  //Et voila, we've filled 'em all

This is like filling each locker with a piece of integer treasure. The numbers within the square brackets are the locker indexes and the ones to the right of the equals’ sign are the values we are storing. You’re essentially saying, “Locker number 0, store the number 10 for me”. Pretty neat, right?

And that, folks, is how you use arrays in C#. Stay tuned for the plot twist – Lists in C# up next!

What is a List in C#?

Okay, if arrays are like ‘fixed lockers’, how would you like a change? Can we get some more adaptable, flexible? Cue in Lists – arrays’ cool cousins who are a bit rebellious. Fancy stuff, right?

Lists in C# are like dynamic collections or, in simpler terms, a cool band of elements clutching onto the same data type. Unlike our good old arrays, these step up the game by allowing adding or removing of elements during runtime! gasp Like arrays, each list item is also cozying up with an index starting from zero.

In our upcoming deep dive, let’s find out how to declare, add elements, and more on Lists in C#.

How a List works in C#?

Alright, fasten your seatbelts, folks. Time to learn to make Lists in C#, which is a bit like shopping but without burning a hole in your pocket.

Initiate a list using this snappy syntax:

List<int> listOInts = new List<int>();

You’re creating an empty list named listOInts, all set and ready to hold integers. It’s like you’ve created an empty bag to put your shopping goodies in.

But how do you fill this bag, or, how do you add elements to your list? In comes the Add() method, the shopping assistant of lists. Observe:

listOInts.Add(100); //Add 100 to the list
listOInts.Add(200); //Add 200 next
listOInts.Add(300); //... and 300
listOInts.Add(400); //... keep 'em coming
listOInts.Add(500); //Fin, last one in!

Wow, we just filled our list with integers! The Add() method takes an integer and appends it to the end of the list. The result, you’ve bagged 5 fancy integers.

That’s the wonder of Lists in C#, my dear friends. Buckle up for more insights on Array vs List showdown. Stay tuned!

Performance Array vs List

Hold on to your hats, folks, now we’re getting into the nitty-gritty – performance! It’s the battle of the century: Array vs List. Let’s find out who outperforms whom and where. Spoiler alert: They both have their moments of glory.

Generally, if we’re talking pure speed for accessing individual elements, arrays have an edge. It’s like arrays have shortcuts to each locker. But when it comes to adding or removing elements? Lists steal the show.

Why is that, you ask? Let’s take a closer look.

Deep Dive into Performance

For Array, accessing an element is pretty fast, a constant-time operation to be precise, no matter where our element sits. Imagine having a direct flight route – super quick and convenient, right? However, adding or removing data is a different ball game altogether.

You must resize the entire array which is just like relocating all your furniture because you bought a new sofa. Yikes.

For List, it’s somewhat opposite. Adding or removing elements is more efficient. Thankfully, lists require resizing only when they are at full capacity, making them the darling when it comes to dynamic data manipulation.

Imagine a train which can add or remove coaches as needed – pretty handy, huh?

Array vs List Access Speed

Let’s examine the access speed factor using a simple illustrative example:

int[] arr = new int[1000000];
int resArr;
for(int i = 0; i < arr.Length; i++) //Filling the array
    arr [i] = i;
//Accessing the elements of the array
Stopwatch sw = Stopwatch.StartNew(); //Initiate stopwatch
for(int i = 0; i < arr.Length; i++)
    resArr = arr[i];
sw.Stop(); //Stop stopwatch
Console.WriteLine("Array access time: "+ sw.ElapsedMilliseconds +" ms");
List<int> list = new List<int>(1000000);
int resList;     
for(int i = 0; i < 1000000; i++)    //Filling the list
//Accessing the elements of the list
sw = Stopwatch.StartNew(); //Initiate stopwatch again
for(int i = 0; i < list.Count; i++)
    resList = list[i];
sw.Stop(); //Stop stopwatch
Console.WriteLine("List access time: "+ sw.ElapsedMilliseconds +" ms");

Notice how arrays have an edge over lists when accessing array elements?

Head-to-Head Comparison: Array vs List

Now, let’s stack each of them up against each other and look at this through a wider lens, considering not just access speed, but also memory usage and insert/delete speed.

Data StructureAccess SpeedMemory UsageSpeed of Insert/DeleteScalabilityPractical Cases
ArrayFast (Direct)Lower (Pre-defined size)Slow (Needs resizing)Fixed (No size variations)Use when data size is fixed and unchanging, e.g. pixels in an image
ListSlower (Sequential)Higher (Dynamic size)Fast (Dynamic re-allocation)Flexible (Can grow/shrink)Use with dynamic data, e.g. in-game players, log records

Still has all the essentials – Array’s speed, List’s flexibility, and a hint of practical application sprinkled in!

What can we conclude? Lists are like adaptable but a little slow athletes, best when the game rules keep changing. Arrays, on the other hand, are those speedy sprinters who are sticklers for routine. Depending on your needs, pick your player!

Memory Management: Array vs List

Next up on the list, let’s talk about memory, the precious real estate of programming. And, in this field, how do Arrays and Lists fare? Spoiler, they play the game fairly differently.

As of general rule, Arrays tend to be more frugal with memory compared to Lists. Arrays don’t have any extra fluff, like keeping track of collection capacity. It’s like Arrays are those cool minimalistic studio apartments, only what you absolutely need.

But hold on, Lists have a trick up their sleeve.

The Memory Game in Detail

Let’s understand this better.

Arrays have a stubborn fixed size. Make an array too large, and it’s like booking a banquet hall for a dinner for two. Talk about wasted space!

Lists, however, are more like pop-up tents – they adjust their size as needed. You can add or remove elements, and the List adapts its size accordingly, providing a more efficient use of memory.

Array vs List Memory Consumption

But don’t just take our word for it. Let’s put this to the test:

int[] numbersArr = new int[100];   //Array with 100 spaces
List<int> numbersList = new List<int>(100);  //List with potential capacity for 100 spaces

// Fill both collection with 50 elements
for(int i = 0; i < 50; i++)
    numbersArr [i] = i;

// Get memory size of both collections
long sizeArr = GC.GetTotalMemory(false);  //Before initiating garbage collector
long sizeList = GC.GetTotalMemory(true);  //After initiating garbage collector

Console.WriteLine("Array size: "+ sizeArr +"bytes");
Console.WriteLine("List size: "+ sizeList +"bytes");

Observe the memory usage. See how array ends up using more memory than List?

Memory Showdown: Array vs List

Alright, it’s time for another head-to-head. Let’s see who’s the leader in the Memory game.

Data StructureMemory UsageUnused MemoryMemory Adaption
ArrayLess (No extra metadata)Can waste if size overestimatedSize fixed at initialization
ListMore (Includes metadata)Efficient due to dynamic sizingAdapts size as per need

In the memory stadium, Lists have the edge in adaptability, while Arrays outshine with leaner usage. As always, choose your contender based on the circumstances!

When to use an Array in C#

In the wild world of C#, the Array is best used in some specific scenarios. So, where do these static, lean memory beasts shine? Read on!

Arrays, in essence, are like your reliable old friends, they’re consistent. This makes them fantastic candidates when you know exactly how many elements you are dealing with right at the beginning and aren’t going to add or remove stuff as you go. They’re also speed demons when it comes to accessing individual elements.

But enough of the jargon, let’s look at some real-life examples!

Real-Life Applications of Arrays

Imagine you’re hosting a game show where you have to keep track of scores of each round for a fixed number of contestants. We know the number of competitors won’t change, hence, an Array is a perfect choice.

int[] scores = new int[5]; //we have 5 contestants

Doing math operations with fixed values? Say, those pesky Matrix Multiplications or a collection of Fibonacci numbers. Lean on the good, steady Arrays to do your bidding stead-fast.

int[] fibNumbers = new int[10]; // Fibonacci sequence of first 10 numbers

Planning to do heavy operations on all the elements? Maybe sort a collection of grades or search for the highest score. Arrays got you covered.

int[] grades = new int[100]; // Grades of a classroom of 100 students.
Array.Sort(grades); // Sorting made easy

Arrays are also excellent for storing constants or for when you need to have direct access to elements. Think lookup tables or a grid of pixels in an image.

Color[,] imagePixelColors = new Color[width, height]; // Storing pixel data of an image

Arrays might seem like your average Joe of data structures, but they pack quite a punch when leveraged properly. Embrace the power of steady, reliable Arrays for your fixed, high-speed element access needs!

Always remember, “With great power comes… well, you know the rest!”

When to use a List in C#

Oh Lists, the adaptable acrobats of programming! In the C# universe, they’re the ones you turn to when you need the freedom to dance – add, remove, grow, and shrink – during runtime.

A List in C# isn’t just useful, it’s a dynamic hero for operations involving addition or removal of elements. Building a vibrant user interface or dealing with a fluctuating data collection? Call up your trusty Lists!

Curious about real-life examples? Buckle up!

Real-Life Applications of Lists

Imagine you’re building an real-time game, where players can join and leave the game anytime. The number of players changes constantly, so a List can perfectly track the current players.

List<Player> players = new List<Player>(); //List to hold Player objects

Working with a list of users in a database? Consider, a Social Networking App where the number of friends a person makes, varies dynamically. Or an E-commerce inventory where products keep getting added and sold out. The all-rounder List is the ultimate champion here!

List<User> users = new List<User>(); //List for User objects
List<Product> inventory = new List<Product>(); //List for Product objects

How about building a cool new web page loaded with tons of UI components which user can add or remove dynamically? Ta-da, Lists enter the scene.

List<UIComponent> uiComponents = new List<UIComponent>(); //List for UI components

In all these situations, you need something robust yet flexible, something that can grow and shrink on demand, something… like a List!

So, the next time you’re working on that cool new feature or the next big app: remember the List, your dynamic partner for all those flashy, ever-changing scenarios. Use it wisely and it can do wonders, just like a magic trick! Abracadabra anyone?

Converting between Arrays and Lists

In some cases, you may need to convert between arrays and lists to take advantage of the benefits of each data structure. In C#, you can convert an array to a list using the ToList() method, like so:

int[] numbers = {1, 2, 3, 4, 5};
List<int> numberList = numbers.ToList();

You can also convert a list to an array using the ToArray() method, like so:

List<int> numberList = new List<int>{1, 2, 3, 4, 5};
int[] numbers = numberList.ToArray();

Array vs List: Pros and Cons

Alright, let’s roll up our sleeves and dive deeper into the advantages and pitfalls of using arrays and lists in C#. Great power comes with great uniqueness – and this absolutely holds true for our programming tools. It’s not all roses you see, but they each have their unique charms.

Array Advantages

  • Predictable memory usage: Knowing the exact amount of memory your data structure will consume can be a lifesaver, especially in memory-constrained devices or high-performance applications.
  • Superfast element access: With direct access to the elements using their indices, Arrays are like those express highways, taking you where you want to go in no time.
  • Operations bliss on entire collection: Whether you’re sorting, searching or by any chance using Array.ForEach() to process each element, Arrays stand tall and make it a cakewalk.

Array Disadvantages

  • No resizing at runtime: This is akin to having a fixed size of pizza – it doesn’t matter how hungry or not you are, the size just won’t change. This lack of flexibility can become a challenge with dynamic datasets.
  • Potential memory wastage: If you go overboard and declare more size than necessary, it’s like renting a mansion for one person. Memory wastage is real, folks!

List Pros Advantages

  • Dynamic size dynamism: Lists are flexible. They can grow or shrink depending on how many elements you want to store, ensuring efficient use of memory.
  • Lightning-fast element addition and removal: Since you don’t need to shift all elements like in an array, adding or removing elements from a List is like snap of fingers.
  • Flourish with fluid data: Lists are your best bet when dealing with data collections that have mood swings – adding, updating, deleting, they handle it all.

List Disdvantages

  • Relatively slower individual element access: Accessing individual elements in the List can be slower compared to an Array. It’s not they’re turtles, but Arrays are just cheetahs.
  • Slightly heavier on memory: Since, Lists carry some additional metadata about their size and capacity, they tend to consume a bit more memory than an Array.

Remember, every data structure has its pros and cons. The key to good programming is understanding these and knowing when and where to use each structure effectively. Don’t forget, One size doesn’t fit all… especially in programming!


In conclusion, arrays and lists are both useful data structures in C# that have their own unique benefits and drawbacks. Choosing the right data structure for your project depends on your specific use case and performance requirements. By understanding the differences between arrays and lists, you can write more efficient and effective code in C#.


  1. Can you add elements to an array after it has been declared?
  • No, the size of an array is fixed at the time of declaration.
  1. Can you remove elements from an array during runtime?
  • No, the size of an array is fixed and cannot be changed during runtime.
  1. Can you access elements of a list using an index?
  • Yes, elements of a list can be accessed using an index starting from 0.
  1. Which data structure is faster: arrays or lists?
  • Arrays are generally faster when it comes to accessing individual elements, while lists are faster when it comes to adding or removing elements.
  1. When should you use an array in C#?
  • Arrays are useful when you know the exact number of elements you need to store and you do not need to add or remove elements during runtime.

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