Introduction and Application of arrays

What are arrays and why did they come in picture?

Suppose, we need to see the average temperature observed in a month: Ideally, you create 30/31 variables; scan each variable value, take sum, and then average it out.

Now consider if you have to average out the temperatures over 6 months or a year or more. It sounds crazy right, to scan 365 or more values, operate on them, and give the result? Also, in practical applications, the data involved is huge.

Arrays come to our rescue!

Arrays are nothing but a collection of items of the same data type having a fixed size.

It is a collection of similar data elements.
These elements are stored in consecutive or contiguous blocks of memory.
It is a derived data type.
The memory locations where these items are stored are referenced to by index or subscript. Index is an ordinal number of the element beginning from the starting location of array.
An array is referenced by a single name or variable.
Array representation in memory is as shown below: Consider an array of temp (temp standing for temperatures)
Above is an array of 5 elements, with index starting from 0 to 4.

Declaration of Array:

As we have seen that every variable needs to be declared before usage, similarly arrays in C also need to be declared.

Declaring an array has the following components:

data_type: what kind of value will be stored. for e.g: marks are of int data type, percentage to be stored will be float data type, grade would be char data type, etc.
array_name: The name using which the array will be identified. e.g: marks, temp etc.
array_size: the number of elements that the array would comprise of.

Syntax:

data_type array_name[array_size];

Example:

float temp[5];  // the statement declares an array called temp of float data type comprising of maximum  5 elements.

Here, the first element of the array would be denoted as temp[0] , next element temp[1] and so on and so forth.

Since indexing starts from 0, the nth element here 5, will be stored at n-1 th i.e 4th position.

int marks[20];  // the statement declares an array called marks of integer data type comprising of maximum  20 elements.
char grades[10]; // the statement declares a char array which can hold a total of 10 elements.

Advantages :

A convenient way to store large amounts of similar data.
It is used to represent multiple items of similar nature using a single name.
It allows us to store data in multi-dimensional arrays. ( We will learn about them in a later section.)
It is used to create other data structures like heaps, linked lists, etc.
You need not access elements sequentially, random access is allowed.
Since elements are stored in consecutive blocks hence they are useful to use in iterations.
Since the size of the array is known during compile-time, there is no chance of memory runout for arrays.

Disadvantages:

Since it is a static data structure that is has a fixed size we should know or determine array size at compile time itself. No modifications can be done to array size during runtime.
Inserting and deleting elements from an array is a tedious task, as it would involve shifting of some or all the elements of the array which would also involve managing memory space for it as well.
No element can be appended after the end of an array.
Since we declare array at compile time itself with a particular size, it is possible that a lot of memory space might get wasted if only some address space is used and occupied.
Operations like insertion, deletion are time-consuming tasks on arrays.

Applications of an array:

Apart from being widely used in programming, arrays have additional applications as well:

Used in mathematical problems like matrices etc.
They are used in the implementation of other data structures like linked lists etc.
Database records are usually implemented as arrays.
Used in lookup tables by computer.
It effectively executes memory addressing logic wherein indices act as addresses to the one-dimensional array of memory.