# Sum of even elements of an Array using Recursion

Given an array arr[] of integers, the task is to find the sum of even elements from the array.

Examples:

Input: arr[] = {1, 2, 3, 4, 5, 6, 7, 8}
Output: 20
2 + 4 + 6 + 8 = 20
Input: arr[] = {4, 1, 3, 6}
Output: 10
4 + 6 = 10

Approach: Write a recursive function that takes the array as an argument with the sum variable to store the sum and the index of the element that is under consideration. If the current element at the required index is even then added to the sum else do not update the sum and again call the same method for the next index. The termination condition will be when there is no element left to consider i.e. the passed index is out of the bounds of the given array, print the sum, and return in that case.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Recursive function to find the sum of``// even elements from the array``void` `SumOfEven(``int` `arr[], ``int` `i, ``int` `sum)``{` `    ``// If current index is invalid i.e. all``    ``// the elements of the array``    ``// have been traversed``    ``if` `(i < 0) {` `        ``// Print the sum``        ``cout << sum;``        ``return``;``    ``}` `    ``// If current element is even``    ``if` `((arr[i]) % 2 == 0) {` `        ``// Add it to the sum``        ``sum += (arr[i]);``    ``}` `    ``// Recursive call for the next element``    ``SumOfEven(arr, i - 1, sum);``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 1, 2, 3, 4, 5, 6, 7, 8 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``int` `sum = 0;` `    ``SumOfEven(arr, n - 1, sum);` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach``import` `java.util.*;``import` `java.lang.*;``import` `java.io.*;` `class` `GFG``{` `// Recursive function to find the sum of``// even elements from the array``static` `void` `SumOfEven(``int` `arr[],    ``                      ``int` `i, ``int` `sum)``{` `    ``// If current index is invalid i.e. all``    ``// the elements of the array``    ``// have been traversed``    ``if` `(i < ``0``) ``    ``{` `        ``// Print the sum``        ``System.out.print(sum);``        ``return``;``    ``}` `    ``// If current element is even``    ``if` `((arr[i]) % ``2` `== ``0``)``    ``{` `        ``// Add it to the sum``        ``sum += (arr[i]);``    ``}` `    ``// Recursive call for the next element``    ``SumOfEven(arr, i - ``1``, sum);``}` `// Driver code``public` `static` `void` `main (String[] args) ``              ``throws` `java.lang.Exception``{``    ``int` `arr[] = { ``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8` `};``    ``int` `n = arr.length;``    ``int` `sum = ``0``;` `    ``SumOfEven(arr, n - ``1``, sum);``}``}` `// This code is contributed by nidhiva`

## Python3

 `# Python3 implementation of the approach` `# Recursive function to find the sum of``# even elements from the array``def` `SumOfEven(arr, i, ``sum``):` `    ``# If current index is invalid i.e. ``    ``# all the elements of the array``    ``# have been traversed``    ``if` `(i < ``0``):` `        ``# Print the sum``        ``print``(``sum``);``        ``return``;` `    ``# If current element is even``    ``if` `((arr[i]) ``%` `2` `=``=` `0``):` `        ``# Add it to the sum``        ``sum` `+``=` `(arr[i]);` `    ``# Recursive call for the next element``    ``SumOfEven(arr, i ``-` `1``, ``sum``);` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[ ``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8` `];``    ``n ``=` `len``(arr);``    ``sum` `=` `0``;` `    ``SumOfEven(arr, n ``-` `1``, ``sum``);` `# This code is contributed by PrinciRaj1992`

## C#

 `// C# implementation of the approach``using` `System;``    ` `class` `GFG``{` `// Recursive function to find the sum of``// even elements from the array``static` `void` `SumOfEven(``int` `[]arr, ``                      ``int` `i, ``int` `sum)``{` `    ``// If current index is invalid i.e. all``    ``// the elements of the array``    ``// have been traversed``    ``if` `(i < 0) ``    ``{` `        ``// Print the sum``        ``Console.Write(sum);``        ``return``;``    ``}` `    ``// If current element is even``    ``if` `((arr[i]) % 2 == 0)``    ``{` `        ``// Add it to the sum``        ``sum += (arr[i]);``    ``}` `    ``// Recursive call for the next element``    ``SumOfEven(arr, i - 1, sum);``}` `// Driver code``public` `static` `void` `Main (String[] args)``{``    ``int` `[]arr = { 1, 2, 3, 4, 5, 6, 7, 8 };``    ``int` `n = arr.Length;``    ``int` `sum = 0;` `    ``SumOfEven(arr, n - 1, sum);``}``}` `// This code is contributed by Rajput-Ji`

## Javascript

 ``

Output
`20`

Time Complexity: O(n), where n is the size of the given array.
Auxiliary Space: O(n), due to recursive call stacks.

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