std::partial_sum is an STL algorithm to calculate the partial sums of a container.


#include <algorithm>

#include <cassert>

#include <numeric>

#include <vector>



int main()

{

  //Create a std::vector with five ones

  const std::vector<int> v(5,1);



  assert(v[0] == 1);

  assert(v[1] == 1);

  assert(v[2] == 1);

  assert(v[3] == 1);

  assert(v[4] == 1);



  //Create a std::vector with the partial sums of five ones

  std::vector<int> w;

  std::partial_sum(v.begin(),v.end(),std::back_inserter(w));



  assert(w[0] == 1); // 1

  assert(w[1] == 2); // 1 + 1

  assert(w[2] == 3); // 1 + 1 + 1

  assert(w[3] == 4); // 1 + 1 + 1 + 1

  assert(w[4] == 5); // 1 + 1 + 1 + 1 + 1



  //Create a std::vector with the partial sums of 

  //the partial sums of those five ones

  std::vector<int> x;

  std::partial_sum(w.begin(),w.end(),std::back_inserter(x));



  assert(x[0] == 1); // 1

  assert(x[1] == 3); // 1 + 2

  assert(x[2] == 6); // 1 + 2 + 3

  assert(x[3] == 10); // 1 + 2 + 3 + 4

  assert(x[4] == 15); // 1 + 2 + 3 + 4 + 5

}

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(C++) std::partial_sum