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Lesson 10 - Multidimensional arrays in the C language

Until now, we've only worked with single-dimensional arrays in the C language. We can imagine a single-dimensional array as a row of boxes in computer memory.

Array structure in the C language

(An array of eight numbers can be seen in the image)

Although it's not too common, you may sometimes encounter multidimensional arrays. Especially, when it comes to game applications. They can be used for things like representing a game area or matrices in mathematics.

Two-dimensional array

A good representation of a 2-dimensional array is a grid because, technically, it is one. A practical application for 2-dimensional arrays would be to use them to store the available seats in a cinema. Here's a visual representation of what I'm referring to:

The 2d array structure in the C language

(We can see the available seats of the cinema in the picture )

Of course, a cinema would be bigger in real life, but this array is just fine as an example. 0 means the seat is available, whereas, 1 means that isn't. Later on, we could also add 2 for reserved seats and so on. It would be more appropriate to create some constants for these states, but we'll get into that later. For now, we'll work with numbers.

In the C programming language, we declare 2D arrays like this:

int cinema[5][5];
int i, j;
// filling with zeros
for (j = 0; j < 5; j++)
    for (i = 0; i < 5; i++)
        cinema[j][i] = 0;

We have to remember to initialize the array with zeros first since we can be never sure which values are in a new array in the C language. It's also important to think about (and ideally to write down as a comment) what is the order of the coordinates. In our case, the first number will index the column and the second one will index the row.


Let's fill the cinema room with 1s like in the picture above. Since we're rather lazy, as good programmers should be, we'll use for loops to create a row of 1s :) We have to enter two coordinates to access an item of the 2D array.

cinema[2, 2] = 1; // center
for (i = 1; i < 4; i++) // fourth row
    cinema[i][3] = 1;
for (i = 0; i < 5; i++) // the last row
    cinema[i][4] = 1;

The output

We'll print the array using a loop as we did before. We'll need 2 loops for the 2d array, the first one will iterate over columns and the second one over rows).

We'll nest the loops in order so the outer loop can iterate over the rows and the inner one over the columns of the current row. After printing a row, we must break a line. Each loop must have a different control variable:

for (j = 0; j < 5; j++)
    for (i = 0; i < 5; i++)
        printf("%d", cinema[i][j]);

The result:

Console application

Nth-dimensional arrays

Sometimes, it may be useful to create an array of even more dimensions. We can all at least imagine a 3D array. Adding to the cinema analogy, we'll say ours has multiple floors or generally more rooms. The visualization could then look like this:

The 3D array structure in the C language

We are able to create a 3D array the same way we created the 2D array:

int cinemas[5][5][3];

The code above creates the 3D array as you saw in the picture. We can access it through the indexer, square brackets, as before, but now we have to enter 3 coordinates.

cinemas[3][2[1] = 1; // the cinema on the second-floor, the third row, the fourth seat

Shortened initialization of multidimensional arrays

I'll also mention that even multidimensional arrays can be initialized with values directly (the following code creates and initializes a crowded cinema room as you can see in the picture):

int cinema[5][5] = {
    { 0, 0, 0, 0, 1 },
    { 0, 0, 0, 1, 1 },
    { 0, 0, 1, 1, 1 },
    { 0, 0, 0, 1, 1 },
    { 0, 0, 0, 0, 1 }

(The array in this code is rotated since we define columns which are declared as rows here).

Jagged arrays

We've mainly talked about rectangular arrays until now. The C language doesn't allow us to create an array of different lengths of inner arrays in each dimension statically. However, it would look like this:

Jagged arrays in the C programming language

Of course, we're able to create even arrays like these, but we have to remember the number of items in each dimension since C doesn't remember that. It's also necessary to allocate memory dynamically. Therefore, we'll leave this topic to the advanced C programming courses.

In conclusion, I would like to add that some people who can't use objects properly use 2D arrays to store multiple sets of data of a single entity. For example, imagine that we want to store the length, width, and height of five cell phones. Although you may think that a 3D array would be best for the situation, it can be pulled off with an ordinary 1D array (specifically a list of objects of the PHONE type). We'll go over all of that in the object-oriented programming course. If you feel like you could still use some more practice, go ahead and give the exercises for this lesson a shot.

In the next lesson, Mathematical functions in the C language - The Math library, we'll look at basic math functions and the math.h library.



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Article has been written for you by David Capka
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