std::valarray::operator[]

// valarray::operator[] example
#include <iostream>     // std::cout
#include <valarray>     // std::valarray, std::slice, std::gslice
int main ()
{
  std::valarray<int> myarray (10);             //  0  0  0  0  0  0  0  0  0  0
  // slice:
  myarray[std::slice(2,3,3)]=10;               //  0  0 10  0  0 10  0  0 10  0
  // gslice:
  size_t lengths[]={2,2};
  size_t strides[]={6,2};
  myarray[std::gslice(1, std::valarray<size_t>(lengths,2), std::valarray<size_t>(strides,2))]=20;
                                               //  0 20 10 20  0 10  0 20 10 20
  // mask:
  std::valarray<bool> mymask (10);
  for (int i=0; i<10; ++i) mymask[i]= ((i%2)==0);
  myarray[mymask] += std::valarray<int>(3,5);  //  3 20 13 20  3 10  3 20 13 20
  //indirect:
  size_t sel[]= {2,5,7};
  std::valarray<size_t> myselection (sel,3);   //  3 20 99 20  3 99  3 99 13 20
  myarray[myselection]=99;
  std::cout << "myarray: ";
  for (size_t i=0; i<myarray.size(); ++i)
	  std::cout << myarray[i] << ' ';
  std::cout << '\n';
  return 0;
}