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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

Syntax of accumulate() function:

accumulate(start, end, initial_sum);

Parameter(s)

• 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

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