Here is very basic description on what is an array. I tried to describe things as simple as possible. This post is meant to be for people who just started programming.

Array

Intuitively you can think that array is a shelf with multiple enumerated drawers, something like this:

.

Yep, it’s that simple. But there is a catch - you can put only one thing into each drawer…

Speaking a bit more formally:

Array is a collection of elements ordered using indexes.

What I can do with an array?

Let’s start from what you can do with shelf?. You can:

• create it (or buy one)
• get thing from a drawer
• change (set) thing which is in some drawer (but remember to keep only one thing there!)
• check how many drawers you have
• etc…

The same with arrays - you can create, get and set elements. There are more operations you can do, but it depends on programming language you use, so we are not going there in this post.

Create an array

Now, it’s time for some code examples.

I decided to go with JavaScript in code snippets, sorry for this!. That’s because you can easily try them in your browser’s console.

Intuitively creating an array is like creating a shelf with drawers. We usually have to tell how many drawers we need, before we can start putting things in them. Or we can just say:

I want to put that thing, this another thing and also that one into my drawers, so please create a shelf in which I can store these things.

To create an array we usually have to just declare it and ascribe it to some variable (in this case it’s called myArray):

    // create an array
    var myArray = new Array("a", "b", "c"); // I want to have a, b and c in my drawers!

    console.log(myArray); // will print ["a", "b", "c"]

In code snippet above myArray is a shelf with drawers indexed from 0 to 2 (because I wanted to have 3 elements in my array):

Beware - arrays are indexed starting from 0 instead of 1 in almost all programming languages (except Pascal).

Access an array

Now you want to check what you put in one of your drawers. For accessing arrays elements usually we use [] in which we put number of index we want to access. Actually, I know only one example of programming language where accessing elements looks differently - Erlang. But for Java, Golang, JavaScript, C++, C, C# and plenty other it is the same.

    var myArray = new Array("a", "b", "c");

    // access first element
    console.log(myArray[0]); // prints a

    // change first element
    myArray[0] = "aa";

    console.log(myArray[0]); // prints aa

So writing myArray[0] means - I want to get this thing, which is in my drawer number 0. Writing myArray[0] = "aa"; means I want to put aa into my drawer number 0.

There are more operations you can do for arrays, but these are the basic ones and the most important ones, so let’s not go further now.

Array in different programming languages

Here are some examples of an array in some other programming languages. I present here how to create an array of five integers (numbers) and how to get and set an element.

Java

In Java declaring array for primitive data types (for example an integer, we don’t want to go further in it, don’t we?) is quite simple - almost the same as in JavaScript. The difference is that you have to declare a type. In this example:

    int[] myArray = {1, 2, 3, 4, 5};
    System.out.println(myArray[0]); // prints 1
    myArray[0] = 11;
    System.out.println(myArray[0]); // prints 11

int[] means that we declare an array of integers. Setting and getting element looks like in JavaScript.

C#

C# in many ways is quite similar to Java. We just need to specify type of our array twice in the declaration, because we need to specify size of our array:

    int[] myArray = new int[5] {1, 2, 3, 4, 5};
    Console.WriteLine(myArray[1]); // prints 2
    myArray[1] = 22;
    Console.WriteLine(myArray[1]); // prints 22

C++

Almost the same as in Java, but in array declaration we have to put square brackets after variable name instead of writing int[] as its type. It’s because memory allocation works a bit differently in C++ (we don’t want to go any further in it, don’t we?).

It’s not necessary to put a number of elements into these square brackets if we declare all elements in an array like this:

    int myArray[5] = {1, 2, 3, 4, 5};
    printf("%d\n", myArray[4]); // prints 5
    myArray[4] = 55;
    printf("%d\n", myArray[4]); //prints 55

Golang

This time number of elements is going to be in square brackets before type declaration, so it’s [5]int:

	myArray := [5]int{1, 2, 3, 4, 5}
	fmt.Println(myArray[2])  // prints 3
	myArray[2] = 3
	fmt.Println(myArray[2]) // prints 33

Python

In Python it’s better to use list instead of array, but still it’s possible to have an array (actually I’ve never used it!). We have to import module array then we can create an array using constructor from this module. This 'i' in array declaration means that we want to have numbers in it. You can put other things in it, check documentation.

    import array

    my_array = array.array('i', [1,2,3,4,5])
    print(my_array[3]) # prints 4
    my_array[3] = 44
    print(my_array[3] # prints 44

Erlang

Erlang is a bit different language, it uses different paradigm - functional one. Anyway the same as in Python, better to use lists instead of arrays.

    %% array with five zeros - [0,0,0,0,0]
    Array = array:new(5, {default, 0}).
    Elem = array:get(0, Array). %% it's 0
    Array1 = array:set(0, 11, Array).
    Elem1 = array:get(0, Array1). %% it's 11

Further reading

To learn more about arrays you can read (and code!) how to:

• check arrays length
• how to iterate over all arrays elements (for example you want to print each of elements in separate line).

I don’t give links here, because I don’t know which programming language you prefer (anyway it doesn’t really matter…). On the other hand being a software developer means that you have to be able to find answers on your own.

If you want to share your discovers or issues - please do so in comments!

Summing up

Here you had a description of what is an array and how it looks like in some programming languages. Next time another important data-structure - list! It’s a bit similar to array, but there are some differences. And it has more of standard operations.

Having some thoughts? Leave a comment!