RxCPP PI Stream

rxcpp_pi.cpp

auto pi_series = []( long limit ){

  return rxcpp::observable<>::range(1, limit)
  .map([](int k) {
    return ( k % 2 == 0 ? -4 : 4 ) / ( long double )( ( 2 * k ) - 1 );
  })
  .sum()
  .as_dynamic();

};
  
pi_series( 1000000 ).subscribe([]( long double total ) {
  std::cout << "Pi: " << total << std::endl;
});

zz_non_rx.cpp

auto pi = [](int k) {
  return ( k % 2 == 0 ? -4 : 4 ) / ( long double )( ( 2 * k ) - 1 );
};
  
long double total = 0;
for( int i = 1; i <= 1000000; ++i ) {
  long double res = pi( i );
  
  total += res;
}
  
std::cout << "Pi: " << total << std::endl;

zzz_output

Pi: 3.14159