std::accumulate() function with example in C++ STL

C++ STL std::accumulate() function: Here, we are going to learn about the accumulate() function in C++ STL with example.
Submitted by Sanjeev, on April 23, 2019

C++ STL supports a variety of functions and templates to solve problems in different ways.

C++ STL std::accumulate() function

std::accumulate() function is used to accumulate all the values in the range [first, last] both inclusive to any variable initial_sum.

Default operation which accumulates function do is adding up all the elements but different operations can be performed.

Syntax of accumulate() function:

    accumulate(start, end, initial_sum);

Here,

start: is the initial position of the iterator
end: is the last position of the iterator.

Note: An additional argument can also be passed in the accumulate function which specifies the type of operation to be performed.

Syntax of accumulate() function with additional argument:

    accumulate(start, end, initial_sum, func);

Here, func is the additional operation which is to be performed.

C++ program to demonstrate example of std::accumulate() function

#include <bits/stdc++.h>
#include <vector>
using namespace std;

int main()
{
	// Initialization of vector
	vector<int> vec{1,2,3,4,5,6,7,8,9};

	// Taking initial sum as 0
	int sum = 0;
	cout << "\n Initial value of sum = " << sum << endl;

	// Demonstration of accumulate function
	// to sum all the elements of the vector
	sum = accumulate(vec.begin(), vec.end(), sum);

	cout << " Value of sum after accumulate = " << sum << endl;

	// Changing value of initial_sum to 50
	sum = 50;

	cout << "\n Initial value of sum = " << sum << endl;

	// Demonstration of accumulate function
	// with the additional argument
	// Here additional argument is used to
	// subtract all the elements from the
	// initial sum. Additional argument can be
	// any valid function or operation
	sum = accumulate(vec.begin(), vec.end(), sum, minus<int>());

	cout << " Value of sum after accumulate function with optional argument = " << sum << endl;

	return 0;
}

Output

 Initial value of sum = 0
 Value of sum after accumulate = 45

 Initial value of sum = 50
 Value of sum after accumulate function with optional argument = 5