C++ Program For Average of an Array (Iterative and Recursive)

Given an array, the task is to find the average of that array. Average is the sum of the array elements divided by the number of elements.

Examples:

Input: arr[] = {1, 2, 3, 4, 5}
Output: 3
Sum of the elements is 1+2+3+4+5 = 15 
and total number of elements is 5.
So average is 15/5 = 3

Input: arr[] = {5, 3, 6, 7, 5, 3}
Output: 4.83333
Sum of the elements is 5+3+6+7+5+3 = 29
and total number of elements is 6.
So average is 29/6 = 4.83333.

1. Iterative Approach

The iterative program is easy. We need to find the sum and divide the sum by the total number of elements.

Approach

1. Iterate each element of an array using a loop.
2. Sum up each element of the array till we reach the end of the array.
3. Divide the sum by the total number of elements and return the average. 

Below is the C++ program to find the average of that array using the Iterative approach:

// C++ program to calculate average
// of array elements
#include <iostream>
using namespace std;

// Function that return average
// of an array.
double average(int a[], int n)
{
    // Find sum of array element
    int sum = 0;
    for (int i = 0; i < n; i++)
        sum += a[i];

    return (double)sum / n;
}

// Driver code
int main()
{
    int arr[] = { 10, 2, 3, 4, 5, 6, 7, 8, 9 };
    int n = sizeof(arr) / sizeof(arr[0]);

    cout << average(arr, n) << endl;
    return 0;
}

6

The complexity of the method above

Time Complexity: O(n), The time complexity of the above code is O(n) as it loops through all elements of the array to calculate the sum. 

Auxiliary Space: O(1), The space complexity is O(1) as no extra space is used.

2. Recursive Approach

The idea is to pass the index of the element as an additional parameter and recursively compute the sum. After computing the sum, divide the sum by n.

Approach

1. We will call the function again and again till we reach the end of an array.
2. We will sum every element of the array and when we reach the end of an array, we will return the average of the array.

Below is the C++ program to find the average of the array using the Recursive approach:

// C++ program to calculate average
// of array elements
#include <iostream>
using namespace std;

// Recursively computes average
// of a[]
double avgRec(int a[], int i, int n)
{
    // Last element
    if (i == n - 1)
        return a[i];

    // When index is 0, divide sum
    // computed so far by n.
    if (i == 0)
        return ((a[i] + avgRec(a, i + 1, n)) / n);

    // Compute sum
    return (a[i] + avgRec(a, i + 1, n));
}

// Function that return average
// of an array.
double average(int a[], int n) { return avgRec(a, 0, n); }

// Driver code
int main()
{
    int arr[] = { 10, 2, 3, 4, 5, 6, 7, 8, 9 };
    int n = sizeof(arr) / sizeof(arr[0]);

    cout << average(arr, n) << endl;
    return 0;
}

6

The complexity of the above program

Time Complexity: O(n)

Auxiliary Space: O(n)

Related Article: Average of a stream of numbers