indirect_array.cpp

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#include <iostream>    // for cout, endl
#include <valarray.h>  // Includes valarray and provides stream inserter.
#include <examples.h>  // Generic header for all examples.
 
typedef std::valarray<int>    valarray_t;
typedef std::valarray<std::size_t> selector_t;
 
int main(void) {
 
  // Create a valarray of integers.
  valarray_t::value_type vbuf[10] = {0,1,2,3,4,5,6,7,8,9};
  valarray_t vi(vbuf, (sizeof vbuf / sizeof *vbuf));
 
  // Create a valarray of indices for a selector.
  selector_t::value_type sbuf[6] = {0,2,3,4,7,8};
  selector_t selector(sbuf, (sizeof sbuf / sizeof *sbuf));
 
  // Print out the valarray<int>.
  std::cout << "original valarray vi\n\n" << vi << "\n\n";
 
  // Print out the selective array.
  std::cout << "vi[0,2,3,4,7,8]\n\n" <<  vi[selector] << "\n\n";
 
  // Double the selected values.
  vi[selector] += vi[selector];
 
  // Print out the modified valarray.
  std::cout << "vi[0,2,3,4,7,8] += vi[0,2,3,4,7,8]\n\n" << vi << std::endl;
 
  return 0;
}