Arrays in Data Structure and Algorithm

Introduction to
Arrays in Data
Structures and
Algorithm
By Kristina Barooah
Computer Science Engineering, Lovely Professional University
Technical Member of GeeksforGeeks-LPU.

What
are Arrays?
Arrays a data structure that can store a fixed-size
sequential collection of elements of the same type.
An array is a collection of variables of the same type
i.e. it stores a collection of data of the same type.
Syntax: Data_type array_name [size];
Example: Int a[5];
Main idea behind having array:
Instead of declaring individual variables, such as
number0, number1, ..., and number99, declaring
one array variable such as numbers and use
numbers[0], numbers[1], and ..., numbers[99] to
represent individual variables is way much easier.

Important
Points about
Arrays
All arrays consist of contiguous memory locations. The lowest
address corresponds to the first element and the highest address to
the last element.
All arrays have 0 as the index of their first element which is also
called the base index and the last index of an array will be total
size of the array minus 1.
A specific element in an array is accessed by an index.
Usage: Arrays are commonly used in computer programs to organize
data so that a related set of values can be easily sorted or searched.
Also, used to Implement other data structures like Stacks, Queues,
Heaps, Hash tables, etc.

Declaration of Arrays
In C/C++, an array can be declared by specifying its type and size or by initializing it or by both.
1. Array declaration by specifying size:
int a[10];
2. Array declaration by initializing elements:
int a[] = {10, 20, 30, 40} ;
Here, in case the size of the array is omitted, an array just big enough to hold the initialization is created.
Thus, the compiler creates an array of size 4. And above is same as "int a[4] = {10, 20, 30, 40}"
3. Array declaration by specifying size and initializing elements:
int a[6] = {10, 20, 30, 40};
Here, in case the compiler creates an array of size 6, initializes first 4 elements as specified by user
and rest two elements as 0. above is same as "int a[] = {10, 20, 30, 40, 0, 0}"
An "array declaration" basically means to name the array and specify the type of its
elements. It can also define the number of elements in the array. A variable with array
type is considered a pointer to the type of the array elements.

However it is not the same in other languages!
For instance, in Java the Syntax to Declare an Array is:
 dataType[] a; (or)
 dataType []a; (or)
 dataType a[];
In JavaScript the Syntax to Declare an Array is :
const array_name = [item1, item2, ...]; or
array_name = new Array( 4 ) ;
Note: JavaScript Arrays are Heterogeneous. Unlike many other popular languages, a JavaScript Array can
hold elements of multiple data types, simultaneously
Syntax to Declare an Array, In Python :
Note: Python does not have built-in support for Arrays, but Python lists can be used
instead.
E.g.: carbrands = ["Ford", " Hyundai", "BMW"]
List can contain heterogeneous values such as integers, floats, strings, tuples, lists, and
dictionaries but they are commonly used to store collections of homogeneous objects. Python lists
are mutable sequences.
Note: all these declarations were for Single dimensional arrays only!

Assignment of Arrays: Assigning an array basically means to set the
values of an array after its declaration. The assignment operator (=)
is used to assign the values to each index of an array and often a loop
is used to do the assignment of an array. The assignment of an array is
moreorless the same in all the programming languages.
For example(code in JAVA):
for (int i = 0; i < javaArray.length; i++)
{ javaArray[i] = i;
System.out.print(javaArray[i] + " ");
}
Initialization of Arrays: As the name suggests initialization means
setting the initial values to the array. It is the process of assigning
values to the array elements at the time of declaration itself. Similar
to assignment, initialization is simple and is moreorless the same in all the
programming languages.

Syntax: Datatype array_name [dimensions] = { element1, element2,
….,element N}
{int a[]={33,3,4,5};
for(int i=0;i<a.length;i++)
System.out.println(a[i]);}
Accessing array Elements: Array elements can be accessed randomly by using
an integer index. Since we know, array index starts with 0 and goes till size of array
minus 1, specifying the required index value can help us access its value.
int[] arr = new int[3];
arr[0] = 10;
arr[1] = 20;
arr[2] = 30;
System.out.println(arr[1]);

Types of
Arrays
Single Dimensional
Arrays
Multi-dimensional
Arrays

Single
Dimensional
Array
Single or One Dimensional array is used
to represent and store data in a linear
form. Array having only one subscript
variable is called One-Dimensional array
or 1-D array or Linear array.
Syntax: <data-type> <arrayname> [size];
For example:
int iarr[3] = {2, 3, 4};
char carr[20] = "c4learn";
float farr[3] = {12.5,13.5,14.5};

Multi-Dimensional
Array
Array having more than one subscript variable
is called Multi-Dimensional array. multi-
dimensional
Array is also called as Matrix. The most
common type of multi-dimensional arrays
are the 2D arrays.
The 2-D arrays are used to store data in the
form of table. They are also used to create
mathematical matrices and perform simple
arithmetical calculations.
Syntax: <data-type> <array_name>
[row_subscript][column-subscript];

1. Declaration of Two Dimensional Array:
Syntax: datatype arrayName [ rowSize ] [ columnSize ] ;
For example: int matrix_A [2][3] ;
2. Initialization of Two Dimensional Array:
Syntax: Data type array Name [rows][colmns] =
{{r1c1value, r1c2value, ...},{r2c1, r2c2,...}...} ;
For example: int matrix_A [2][3] = { {1, 2, 3},{4, 5, 6} } ;
3. Accessing Individual Elements of Two Dimensional
Array:
Syntax: Array Name [ row Index ] [ column Index ]
For example: matrix [0][1] = 10 ;

Basic
Operations
• Traverse − print all the array
elements one by one.
• Insertion − Adds an element at the
given index.
• Deletion − Deletes an element at the
given index.
• Search − Searches an element using
the given index or by the value.
• Update − Updates an element at the
given index.

Arrays in Data Structure and Algorithm

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