In this tutorial, we are going to learn about **Multi Dimensional Arrays in C**.

## C Multi Dimensional Arrays:

**C** provides the ability to create **multi dimensional** arrays. Below are a few examples of **multi dimensional arrays**:

**Syntax:**

```
data_type array_name[size_1][size_2][size_3].......[size_n];
//where size_1 to size_n from the dimensions of the declared array
```

Examples:

```
int arr_2d[3][4]; //an example for a two-dimensional array
int arr_3d[3][4][2]; //an example for a three-dimensional array
int arr_4d[3][3][2][4]; //an example for a four-dimensional array
```

**Two-dimensional** and **three-dimensional** arrays are the most common types of multi-dimensional arrays.

A two-dimensional array is used to represent the values in the form of rows and columns.

## Two Dimensional Array:

In a **two-dimensional array,** two sizes are provided. The first subscript represents the **row** size while the second subscript represents the **column** size. The format of declaring a two-dimensional array is Below is an example of a two-dimensional array:

`int arr[2][2];`

In the above declaration, **arr** is the name of the array, which contains 2 **rows** with 2 **columns** each that represent a block of **4** consecutive storage locations.

Where,

**arr[0][0]** and **arr[0][1]** represent the elements in the **0**^{th} row

**arr[1][0]** and **arr[1][1]** represent the elements in the **1**^{st} row

Each element of a two-dimensional array is accessed by its **row** and **column** index.

Let us consider an example of a two-dimensional array:

int arr[2][2]; //declares an array with 2 rows and 2 columns representing a block of 4 consecutive storage locations

In the above example, the array variable **arr** contains the **base address** of the entire array. Let us assume the base address as some random number: **1024**.

The formula for finding the location of the element in the **i**^{th} **row** and **j**^{th} **column** is :

```
Address of the ith row and jth column element
= *(base_address + i) + j
= base_address + i * total_columns * scale_factor + j * scale_factor
```

Using the above formula, the location of arr[0][1] can be calculated as below:

```
*(arr + 0) + 1 //where 0 is the row's index and 1 is the
column's index = 1024 + 0 * total_columns * [scale_factor] + 1 * [scale_factor]
= 1024 + 0 * 3 * 2 + 1 * 2
= 1024 + 0 + 2
= 1026
```

In the above line, **2** is the size of the data type **int** in 16-bit machines. **2** is also referred to as a scale factor.

The **scale factor** is automatically calculated by the system, which is a value representing the size of the data type of the array.

**Note:** In the below program, the code snippet ***(num + i) + j** is used to find the address of **i**^{th} **row** and **j**^{th} **column**, and the code snippet *** (*(num + i) + j)** is used to find the value at **i**^{th} **row** and **j**^{th} **column**

## Three Dimensional Array:

A **three dimensional array** can be visualised as an array of two-dimensional arrays. The 3-D array can also be visualized as **pages** containing a 2-D array with elements in rows and columns.

Below is an example of a three-dimensional array:

Syntax:

`data_type array_name[size_1][size_2][size_3];`

Example declaration:

`int arr[2][2][2];`

For example, the above 3-D array can be visualized as 2 pages, each containing a 2-D array of 2 rows and columns each, totaling 8 elements, which are stored in consecutive storage locations.

## Initialization of arrays:

The **elements of an array** can also be **initialized** with the values during **declaration** instead of reading them by the I/O functions.

Note that an **array** can be initialized in its declaration only. The lists of values should be enclosed within **braces**. The values should be separated by commas and must be **constants** or **constant expressions**.

A one-dimensional array can be initialized as,

int a[5] = {10, 20, 30, 40, 50};

The values within the braces are scanned from left to right and assigned to **a[0]**, **a[1]**, **a[2],** **a[3], **and **a[4]** respectively.

A **two-dimensional** array can be initialized as,

int a[2][2] = {{10, 20}, {30, 40}};

Here, the values within the inner braces are assigned as elements to each **row**. If the number of values initialized for an array is **less than** the size mentioned, the missing elements are assigned to **zero**.

For example in

int a[3][4] = {{1, 2}, {3, 4, 5}};

the elements **1** and **2** are stored in **a[0][0]**, **a[0][1]** of the **0**^{th} row and elements **3, 4** and **5** are stored in **a[1][0]**, **a[1][1]** and **a[1][2]** of the **1**^{st} row respectively. All the other elements are initialized to **zero**.

In the example, int a[3][4] = {1, 2, 3, 4, 5};, the values or elements **1, 2, 3, 4** and **5** are assigned starting from left-side to **a[0][0]**, **a[0][1]**, **a[0][2]**, **a[0][3]** and **a[1][0]** respectively.

## Some Special Points:

Below are some important points to remember regarding **arrays**:

- An array is a
**derived data type**. - It can store one or more elements of the
**same data type**. - An element in an array can be referred to as
**arr**[**index**], where**arr**is the name of the array and an**index**is an integer constant that specifies the location of the element in the array. - An array
**subscript (index)**always starts at**zero**. Hence, it is said that the array uses zero-based addressing. The**last**element’s**index**is always.**size-1** - Elements within an array are stored in
**consecutive memory locations**. - The array name holds/stores the starting memory location of the
**array**, this address is known as the**base address**of the array. - Arrays can be
**one-dimensional**or**multi-dimensional**. - Array declaration must contain the size without fail.
- The array
**size**must be of**integer type**which is greater than zero. - In a multi-dimensional array, each dimension uses a separate pair of square brackets.
- It is a good programming practice to mention the size using
**symbolic constants**which facilitate easier program maintenance. - It is
**illegal**to refer to the elements that are**out of the array bounds**. For an array, a[10], the array bounds are from**a[0]**to**a[9]**only. The**subscript**or**index**values other than values between 0 to 9 are**illegal**hence will throw an error saying the array access is out of bounds. - In
**C**the compiler does not check on the**bounds of an array**, hence we will see an error only during execution.

## REFERENCES:

Happy Learning 🙂

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