Lists and Arrays: When to Use Which? (Simple Explanation)

Hello everyone! How are you, are you well? As you know, sometimes in the world of programming, things happen that make you go ‘Wow, what is this now?’. Arrays and lists were a bit like that for me at the beginning. It’s like they are two siblings, but with very thin yet crucial differences between them. Anyway, let’s not prolong the talk and get straight to the point.

Now imagine you went to a supermarket. You have a shopping list in your hand. What’s on this list? Milk, cheese, bread, eggs… Okay, the list is nice but don’t you need to put these items in your shopping cart? That’s where arrays and lists come into play.

First, let’s start with arrays. Arrays are structures that store fixed-size, same-type elements. So, when you create an array, you might say, ‘I want 10 integers in this array,’ and it’s done. Then you fill it with numbers. But if you say, ‘Oh, I want to add one more,’ it’s trouble! Arrays have a fixed size, which you cannot change. It’s like that old dresser with compartments; whatever space you have, that’s it. If you need more space, you can’t put more items. So, if you know in advance exactly how much data will come, arrays are perfect. For example, if you are developing a game and will keep a list of 10 players, then arrays are excellent.

And what about lists? Lists are more flexible, dynamic structures. What does that mean? You can add or remove elements as you please. It’s like that shopping list: ‘Milk, cheese, bread… Oh, I forgot to buy bananas!’ and you add bananas. Or ‘I decided not to buy that cheese,’ and remove it. That’s what lists do perfectly. For this reason, in, say, scenarios where data size is uncertain or data changes frequently, lists are very useful. For example, if you are storing user comments on a website—comments can come anytime, and old comments can be deleted. In such cases, using a list makes the most sense. In C#, `List` class is an excellent example of this. The ‘T’ can be replaced with any data type you want.

Now, let me share a personal technical disaster I experienced. I was developing a project where users had to fill out a form. The form allowed them to select multiple products. Initially, we thought they would choose a maximum of 5 products and created an array accordingly. But guess what happened? Some users selected 10-15 products! Naturally, our array immediately broke, throwing errors. My own code failed. Luckily, we switched to lists and fixed the problem. That experience made me better understand when to use arrays versus lists.

Honestly, one of the hardest parts I faced when learning these was constantly wondering ‘Should I use an array or a list?’ I realized that it all depends on the need. If fixed size and same data types suffice, arrays are more efficient because memory management is easier. But if flexibility and dynamism are required, lists are the way to go. The performance difference becomes more noticeable with larger data sets, but in smaller projects, it’s less felt.

Suppose you have an app where users save their favorite products. Initially, you thought there would be maybe 5-10 products. So, you created an array. But then you see some users add hundreds of favorite products. That’s when arrays become insufficient. You should then prefer something like `List` or `List`. This makes it easy to add as many items as needed. You can use `Add()` to insert items and `Remove()` to delete them. Isn’t that great?

Another aspect is if you create data once and won’t change it afterwards, arrays might be more suitable. Accessing elements in arrays could be slightly faster than in lists. But again, this performance difference is more evident with large datasets. For small data, it’s hardly noticeable. So, knowing when and what to use makes your code more understandable and efficient.

Let’s illustrate this with some code to make it clearer. Imagine we want to store some names. First, try with arrays, then with lists. Let’s see what happens.

// Arrays have a fixed size. We define a 3-element string array. string[] nameArray = new string[3]; // We have space for only 3 people

nameArray[0] = “Ali”; nameArray[1] = “Veli”; nameArray[2] = “Ayşe”;

// Trying to add a fourth element will give an error! Size exceeded.

Console.WriteLine("Array elements:"); foreach (var name in nameArray) {     Console.WriteLine(name); }

As you see, we added 3 elements and that’s it. Trying to add a fourth will cause an error. Now, let’s look at lists.

Lists are flexible structures that allow us to add more elements at will.

// Lists can change size freely. List nameList = new List();

nameList.Add("Ali"); nameList.Add("Veli"); nameList.Add("Ayşe"); nameList.Add("Fatma"); // Add as many as you want!
Console.WriteLine("List elements:"); foreach (var name in nameList) {     Console.WriteLine(name); }
nameList.Remove("Veli"); // Easily remove an element.
Console.WriteLine("After removing 'Veli', List elements:"); foreach (var name in nameList) {     Console.WriteLine(name); }
And just like that! Lists let you add and remove elements freely, providing significant flexibility. Sometimes, when you think, 'I wish this part was different,' lists come to the rescue. I read more about this topic in an article here, which was quite interesting. Similar examples were given.
In summary, arrays are ideal for fixed-size, same-type data, while lists are better for dynamic, variable-sized datasets. Choosing between them depends entirely on your project's needs. I recommend starting with lists, especially for beginners, because their flexibility reduces initial mistakes. Of course, arrays still have their place, especially where performance is crucial. Both have their strengths :)