Arrays in C++

Introduction to arrays

  • Array is a collection of variables of same type that stores the elements in the sequential manner.
  • It is a data structure.
  • Array elements consist of contiguous memory locations and are accessed randomly using the subscript or index variable.
  • It stores a fixed-size sequential collection of elements of the same type.
  • In array, the lowest address corresponds to first element and highest address corresponds to the last element.

Declaring Arrays

  • To declare an array, first specify the type of the elements and the number of elements required.
  • Syntax:
    datatype arrayname [arraysize];

  • The arraysize must be integer constant greater than 0.
  • Example:
    int empid[5];    //We created array of 5 employees

  • Array index starts from 0.

  • ElementDescription
    empid[0]It represents variable for 1st employee id.
    empid[1]It represents variable for 2st employee id.
    empid[2]It represents variable for 3st employee id.
    empid[3]It represents variable for 4st employee id.
    empid[4]It represents variable for 5st employee id.

Initializing Arrays

Following are the three ways to initialize an Array:

1. Specify size and initialization will be done using the loop.
int empid[5];
for(i=0; i<5; i++)

2. Specify size and initialize array in a single statement.

3. Without specifying size

The above example specifies the size of an array equal to 5.

Consider the following representation:
speciying size array representation

The above representation of an array is the pictorial form of an array, starts with 0.

Accessing Arrays

Example : Program demonstrating the declaring, initializing & accessing the arrays

#include <iomanip>      //used for setw() function
using namespace std;
int main ()
     int a[ 5 ];     // a is an array of 5 integers   
     for ( int i = 0; i < 5; i++ )         // initialize elements of array   
         a[i] = i + 101;          // set element at location i to i + 100
     cout<<"Array Element"<<endl;
     for ( int j = 0; j < 5; j++ )          //for displaying array element
     return 0;

Note : setw() is used to format the output.

Array Element
0 101
1 102
2 103
3 104
4 105

Multi-Dimensional Arrays

  • Multi-Dimensional Arrays are used to store data which requires multiple references.

  • Syntax:
    data-type name [size1] [size2] . . . [size n];

  • If we want to create Two-dimensional array then we can declare it as:int arr[3][3];

  • Where,
    i. First dimension represents the number of rows.
    ii. Second dimension represents the number of columns.

    Consider the below representation of Two-dimensional array:
    two dimensional array diagram
  • The size of the array of the above figure is 3 X 3, but the indices will be from 0 to 2 in both rows and columns because array starts from 0.
  • We can also have an array of more than two dimensions. Three-dimensional array has 3 dimensions, for example int a[2][2][2], but it is rarely used.
  • Two-dimensional array has 2 dimensions. Matrix is the best example of two-dimensional array.
  • It is the simplest form of multi-dimensional array.
  • To initialize the two-dimensional arrays specify the bracketed values for each row.

  • For example:
    int a[3][3] = {
                             {0,1,2},      //Initialize 0th row
                             {3,4,5},     //Initialize 1st row
                             {6,7,8}     //Initialize 2nd row

  • There is another way also to initialize the two-dimensional array:
    int arr[3][2]={1,4,5,2,6,5}

Accessing Two-dimensional Arrays

Example : Program Demonstrating the Two-dimensional Arrays

#include <iostream>
using namespace std;
int main ()
     int arr[2][2] = {{0,0}, {1,2}};  //Two-dimensional array with 2 rows and 2 columns.
     for ( int i = 0; i < 2; i++ )        //Output each array element's value  
     for ( int j = 0; j < 2; j++ )
          cout<<"arr["<< i<<"]["<<j<<"]: ";
          cout<<arr[i][j]<< endl;
     return 0;

arr[0][0]: 0
arr[0][1]: 0
arr[1][0]: 1
arr[1][1]: 2

Passing arrays to the Function

Example: Demonstrating the passing arrays to the function

#include <iostream>
using namespace std;
double getAverage(int marksarr[], int arrsize);     // function declaration
int main ()
      int marks[5] = {60,55,35,40,50}; // integer array with 5 elements.
      double avg;
      avg = getAverage(marks, 5); //passing array to the function as an argument.
      cout <<"Average is: "<<avg<<endl;
      return 0;
double getAverage(int marksarr[], int arrsize)
      int i, sum = 0;       
      double avg;          
      for (i = 0; i < arrsize; ++i)
            sum += marksarr[i];
      avg = double(sum) / arrsize;
      return avg;

Average is: 48