// return size of an array as a compile-time constant. (The
// array parameter has no name, because we care only about
// the number of elements it contains.)
template<typename T, std::size_t N>                 // see info
constexpr std::size_t arraySize(T (&)[N]) noexcept  // below on
{                                                   // constexpr
  return N;                                         // and
}                                                   // noexcept

int keyVals[] = { 1, 3, 7, 9, 11, 22, 35 };      // keyVals has
                                                 // 7 elements

int mappedVals[arraySize(keyVals)];