/* Code for exercise 22.2. |  | "C++ Solutions--Companion to The C++ Programming Language, Third Edition" | by David Vandevoorde; Addison-Wesley 1998; ISBN 0-201-30965-3. | | Permission to use, copy, modify, distribute and sell this software | and its documentation for any purpose is hereby granted without fee. | The author makes no representations about the suitability of this | software for any purpose.  It is provided "as is" without express or | implied warranty. `----------------------------------------------------------------------*/#include <algorithm>#include <iostream>#include <valarray>template<typename T, typename F>void apply(std::valarray<T> &a, F f) {   for (std::size_t k = 0; k!=a.size(); ++k)      a[k] = f(a[k]);}struct Sqr {   double operator()(double a) { return a*a; }};double primes[] = { 2.0, 3.0, 5.0, 7.0, 11.0, 13.0 };int main() {   std::valarray<double> va(primes, sizeof(primes)/sizeof(primes[0]));   std::cout << "va = [ ";   std::copy(&va[0U], &va[0U]+va.size(),             std::ostream_iterator<double, char>(std::cout, " "));   std::cout << "]\n";   apply(va, Sqr());   std::cout << "apply(va, Sqr())\n";   std::cout << "va = [ ";   std::copy(&va[0U], &va[0U]+va.size(),             std::ostream_iterator<double, char>(std::cout, " "));   std::cout << "]\n";   return 0;}