Function main

Examples/Modules/Chapter 09/Ex9_01.cpp:10–28

   std::optional<size_t> start_index = std::nullopt); // or: ... start_index = {});

int main()
{
  const auto string{ "Growing old is mandatory; growing up is optional." };

  const std::optional<size_t> found_a{ find_last(string, 'a') };
  if (found_a)
    std::cout << "Found the last a at index " << *found_a << std::endl;

  const auto found_b{ find_last(string, 'b') };
  if (found_b.has_value())
    std::cout << "Found the last b at index " << found_b.value() << std::endl;

// following line gives an error (cannot convert std::optional<size_t> to size_t)
// const size_t found_c{ find_last(string, 'c') }; 
                                                   
  const auto found_early_i{ find_last(string, 'i', 10) };
  if (found_early_i != std::nullopt)
    std::cout << "Found an early i at index " << *found_early_i << std::endl;
}

std::optional<size_t> find_last(const std::string& string, char to_find, 
                                std::optional<size_t> start_index)