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.

Element	Description
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.
Example:
int empid[5];
for(i=0; i<5; i++)
cin>>empid[i];

2. Specify size and initialize array in a single statement.
Example:
empid[5]={101,102,103,104,105};

3. Without specifying size
Example:
empid[]={101,102,103,104,105};

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<iostream>
#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
     {
         cout<<setw(9)<<j<<setw(13)<<a[j]<<endl;
     }
     return 0;
}

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

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,

Consider the below representation of Two-dimensional array:

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;
}

Output:
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;
}

Output:
Average is: 48