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How to find the sum of values in an array in C++

Sarah Tanveer

In this shot, we will go over how to sum up all the values in a one-dimensional array.

Example of what the algorithm will do

There are two main ways to achieve this, as discussed below.

1. Use a for loop

We can use a for loop to traverse the array. All the elements can be added up one by one:

  1. Initialize sum = 0.
  2. Run a for loop from i = 0 to i = size - 1.
  3. At every iteration of the for loop, add sum and the current element of the array, i.e., sum = sum + arr[i].
  4. At the end of the for loop, the sum of all the elements will be stored in the sum variable.

Dry run of for loop

First iteration of for loop
1 of 5
#include <iostream>
using namespace std;

int main() {
  // initialise array
  int arr[] = {2, 4, 6, 8};
  int size = 4;

  // initialise sum to zero
  int sum = 0;

  // for loop runs from 0 to size - 1
  for(int i = 0; i < size; i++)
  {
    sum = sum + arr[i];
  }

  cout << "The sum of the elements in the array: " << sum;
}

2. Use the accumulate() function

The accumulate() function is defined in the <numeric> header file, which must be included at the start of the code in order to access this function:

accumulate(arr , arr+size , sum);

The function takes three arguments:

  1. arr: The name of the array.
  2. arr+size: The name of the array + size of the array.
  3. sum: The variable in which the sum needs to be stored.

The function returns an int value, which is the sum of all the elements in the array.

#include <iostream>
#include<numeric>
using namespace std;

int main() {
  // initialise array
  int arr[] = {2, 4, 6, 8};
  int size = 4;

  // initialise sum to zero
  int sum = 0;

  // use function
  sum = accumulate(arr, arr+size, sum);

  cout << "The sum of the elements in the array: " << sum;
}

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