lib/accumulate2.cpp

The following code example is taken from the book
C++17 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2017
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <iostream>
#include <vector>
#include <numeric>   // for accumulate()

void printSum(long num)
{
  // create coll with num sequences of 1 2 3 4:
  std::vector<long> coll;
  coll.reserve(num * 4);
  for (long i=0; i < num; ++i) {
    coll.insert(coll.end(), {1, 2, 3, 4});
  }

  auto squaredSum = [] (auto sum, auto val) {
                      return sum + val * val;
                    };
  
  auto sum = std::accumulate(coll.begin(), coll.end(),
                             0L,
                             squaredSum);
  std::cout << "accumulate(): " << sum << '\n';
}

int main()
{
  printSum(1);
  printSum(1000);
  printSum(1000000);
  printSum(10000000);
}