Which C++ Parallel.For expression looks better for a C++ new learner, and more importantly, why?

A C++ learner in 2017 must be exposed to standard library types from the very first day, and not be taught of C as an introduction, because the C supported paradigm is only 1/4 of C++ supported ones and the C idioms don’t match the modern C++ ones. They are two well distinct languages. If you arrive to parallel algorithms, you must have already seen a lambda (because that’s one of the most sane way to instantiate and std::thread or and std::future via an std::async call). Don’t worry about the syntax and punctuation. It may look clumsy to C programmers because they are not accustomed to that. But to a C++ that have already seen the components, that syntax is just putting them together. std::for_each C++ Algorithm library Defined in header algorithm template class InputIt, class UnaryFunction UnaryFunction for_each( InputIt first, InputIt last, UnaryFunction f ); (1) template class ExecutionPolicy, class ForwardIt, class UnaryFunction2 void for_each( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, UnaryFunction2 f ); (2) (since C++17) 1) Applies the given function object f to the result of dereferencing every iterator in the range [first, last), in order. 2) Applies the given function object f to the result of dereferencing every iterator in the range [first, last) (not necessarily in order). The algorithm is executed according to policy. This overload does not participate in overload resolution unless std::is_execution_policy_v std::decay_t ExecutionPolicy is true. read less