Difference between Array and Union in C

In this article, we will discuss about the Array and Union in C. But before discussing their differences, we must know about the Array and Union in C.

What is the Array?

An array is a collection of equivalent data elements that may be referred to by a common name and are stored in different memory regions. Array items can be retrieved using indices. It's important to point out that the components in a single Array must all be of the same data type. Storing items in an Array requires the usage of primitive data types like int, float, double, char, etc., but of the same data type.

Types of Arrays in C:

C has two different kinds of arrays:

Single-Dimensional Arrays: A single-dimensional array is the most basic type of array in C. A 1D array is made up of items of comparable kinds that their indices may access.
Multi-Dimensional Arrays: The most frequently used form of multi-dimensional array in C language is the 2D The total number of dimensions may be greater than two depending on the programming language of the system being used by the user. These arrays are made up of array elements.

Array declaration in C

In C, we must declare the array like any other variables before using it. We may declare an array by defining its name, the type of its components, and the size of its physical dimensions. When we create an array in C, the compiler automatically allocates a memory block of the dimension specified to the array name.

Syntax:

It has the following syntax:

Initialization of an Array in C

In C, initialization is the process of assigning an initial value to a variable. When an array is declared or allocated memory, its elements include some garbage value. As a result, we must set the array's value to something useful. In C, we may initialize an array in several ways.

1. Array Declaration and Initialization

In this process, we initialize the array and declare it. We use an initializer list to initialize numerous array entries. An initializer list is a collection of values contained by braces and separated by a comma.

Syntax:

It has the following syntax:

2. Array declaration without size

When we use an initializer list to initialize an array, we can prevent explaining the size of the array because the compiler can determine the size of the array in these circumstances. In these situations, the size of the array is equal to the number of items in the initializer list because the compiler is capable of determining the size of the array.

Syntax:

It has the following syntax:

What is the Union?

Union is a user-defined datatype that allows the storing of different items in the same memory region. A union can have numerous members, but only one member can hold the value at any one moment. Union is appropriate for several uses that require the same memory space.

Declaration of Union

Syntax:

It has the following syntax:

union name_union
{
 datatype value;
 datatype value;
};

C unions allow data members that are mutually exclusive to make use of the same memory. It is critical when memory is valuable, such as in embedded devices. Unions are typically used in embedded applications where direct memory access is required.

Key differences between Array and Union

There are several differences between the Array and Union in C. Some main differences between the array and union are as follows:

Aspect	Array	Union
Purpose	Arrays are used to hold numerous elements of the same data type in contiguous memory regions.	Unions allow multiple data kinds to share the same memory space while only allowing one member to be functional at a time.
Datatype	Arrays can only carry items of one data type. For example, an array containing numbers, characters, etc.	Unions can store components of many data kinds. For example, a union may include an integer, a float, and a character array.
Memory Allocation	Arrays allocate memory that is contiguous to all items of the same data type.	Each of the members of a union shares a single memory location, and the largest member determines the union's size.
Accessing Elements	Elements are accessible using indices that begin at 0.	In a union, the most recently allocated member can be retrieved.
Size Declaration	The size of the arrays must be defined at compile time and must stay constant during execution.	The largest member of a union determines its size.
Memory Efficiency	Each array member has its own memory area, which may result in greater memory use.	Unions are memory-efficient because members share an identical memory area, but they are limited in continuous usage.
Use Cases	Arrays are suitable for storing collections of comparable data types when access to elements by an index is required, such as a list of numbers or characters.	Unions enable for memory optimization in situations when many data types must share a memory region. For example, they may be used to represent a value that can be an integer, float, or character array-but only a single at a time.