**`std::accumulate()`** is a built-in function in C++'s Standard Template Library. The function takes in a beginning iterator, an ending iterator, initial value, and (by default) computes the sum of the given initial value and the elements in the given range.

The function can also​ be used for [left folding](https://en.wikipedia.org/wiki/Fold_(higher-order_function)). This is done by passing in a binary operation function object that takes the current accumulation value and the value of the current element, and returns the new accumulation value.

Take a look at the function signature of `std::accumulate()` below:

#include <iostream>
// The following library needs to be included to use std::accumulate()
#include <numeric>
#include <vector>

using namespace std;

int main() {
  std::vector<int> v{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  int sum = std::accumulate(v.begin(), v.end(), 0);
  std::cout << sum;
}

## Using `std::accumulate` with a built-in binary predicate

In the following examples, an array of integers are summed and folded:

#include <functional>
#include <iostream>
// The following library needs to be included to use std::accumulate()
#include <numeric>
#include <vector>

using namespace std;

int main() {
  std::vector<int> v{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  int product = std::accumulate(v.begin(), v.end(), 1, std::multiplies<int>());
  std::cout << product;
}

## Using `std::accumulate` with a custom binary predicate

#include <functional>
#include <iostream>
// The following library needs to be included to use std::accumulate()
#include <numeric>
#include <string>
#include <vector>

using namespace std;

int main() {
  std::vector<int> v{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  
  // custom binary predicate
  auto dash_fold = [](std::string a, int b) {
    return std::move(a) + '-' + std::to_string(b);
  };

  std::string s = std::accumulate(
    std::next(v.begin()), v.end(),
    std::to_string(v[0]), // start with first element
    dash_fold
  );

  std::cout << s;
}

What is the std::accumulate() function in C++?

std::accumulate() is a built-in function in C++ s Standard Template Library. The function takes in a beginning iterator, an ending iterator, initial value, and (by default) computes the sum of the given initial value and the elements in the given range. The function can also​ be used for left folding. This is done by passing in a binary operation function object that takes the current accumulation value and the value of the current element, and returns the new accumulation value. Take a look at the function signature of std::accumulate() below: 

What is the std::accumulate() function in C++?

Code

Using `std::accumulate()`

Using `std::accumulate` with a built-in binary predicate

Using `std::accumulate` with a custom binary predicate

What is the std::accumulate() function in C++?

Code

Using std::accumulate()

Using std::accumulate with a built-in binary predicate

Using std::accumulate with a custom binary predicate

Using `std::accumulate()`

Using `std::accumulate` with a built-in binary predicate

Using `std::accumulate` with a custom binary predicate