Even numbers at even index and odd numbers at odd index

Array sum in C++ STL

Last Updated : 14 Feb, 2025

Array sum can be defined as the sum of all elements of an array. In this article, we will learn how to find the array sum using C++ STL.

Examples

Input: arr[] = {5, 10, 15, 11, 9}
Output: 50
Explanation: As 5 + 10 + 15 + 11 + 19 = 50

Input: arr[] = {1, 2, 3, 4, 5}
Output: 15
Explanation: As 1 + 2 + 3 + 4 + 5 = 15

Following are the different STL functions to find the array sum in C++:

Table of Content

Using accumulate()
Using reduce() (C++ 17 Onwards)

Using accumulate()

In C++, STL provide the function std::accumulate() to find the sum of an array elements. It is defined inside the <numeric> header file.

Syntax

std::accumulate(first, last, sum);

where first and last are the iterator to first element and the element just after the last element of the range.

Example

C++

// C++ program to find the array sum using
// of std::accumulate()
#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {5, 10, 15, 11, 9};
    int n = sizeof(arr) / sizeof(arr[0]);

    // Find array sum using std::accumulate()
    cout << accumulate(arr, arr + n, 0);
    return 0;
}

Output

Time Complexity: O(n), where n is the size of the array.
Auxiliary Space: O(1)

Using reduce() (C++ 17 Onwards)

Since C++ 17 onwards, we can use the std::reduce() method to find the sum of all array elements. It is similar to std::accumulate() function and returns the sum of values of elements in the given range. It is also defined inside the <numeric> header file.

Example

C++

// C++ program to find the array sum using
// of std::reduce()
#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {5, 10, 15, 11, 9};
    int n = sizeof(arr) / sizeof(arr[0]);

    // Find array sum using std::reduce()
    cout << reduce(arr, arr + n, 0);
    return 0;
}

Output

Time Complexity: O(n), where n is the size of the array.
Auxiliary Space: O(1)

Even numbers at even index and odd numbers at odd index

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