// “Write a C++ program that prompts the user to enter 5”

#include <iostream>
#include <regex>
#include <string>


std::string rtrim( const std::string& s ) { return s.substr( 0, s.find_last_not_of(" \f\n\r\t\v")+1 ); }
std::string ltrim( const std::string& s ) { return s.empty() ? s : s.substr( s.find_first_not_of(" \f\n\r\t\v") ); }
std::string  trim( const std::string& s ) { return ltrim( rtrim( s ) ); }


int main()
{
  while (true)
  {
    std::cout << "Please enter 5";
    std::string s;
    getline( std::cin, s );

    if (s == std::string( 5, s.c_str()[0] )) break;

    s = trim( s );
    if (s == std::string( 5, s.c_str()[0] )) break;

    if (regex_search( s, std::regex("five|5",std::regex_constants::icase) )) break;
    
    if (regex_match( s, std::regex(R"<>((\S+)(\s+\1){4})<>") )) break;

    if (regex_match( s, std::regex(R"<>([^,;:.\?!]+(\s*[,;:.\?!]\s*[^,;:.\?!]+){4})<>") )) break;

    std::cout << "\nNope. ";
  }
  std::cout << "\nThank you.\n";
}

#include <cmath>
#include <iostream>
#include <numbers>

struct two_t { };
template <class T>
constexpr auto operator^(T base, two_t) { return base * base; }

int main()
{
   using namespace std::numbers;
   constexpr two_t ²;

   std::cout << "The answer is " <<
      (((std::sin(e) ^ ²) + (std::cos(e) ^ ²)) +
       std::pow(e, ln2) + std::sqrt(pi) * inv_sqrtpi +
       ((std::cosh(pi) ^ ²) - (std::sinh(pi) ^ ²)) +
       sqrt3 * inv_sqrt3 * log2e * ln2 * log10e * ln10 *
       pi * inv_pi + (phi * phi - phi)) *
      ((sqrt2 * sqrt3) ^ ²) << '\n';
}

#include <iostream>
#include <string>
#include <ranges>
#include <numbers>

int main()
{
   std::string cat { "cat" };

   std::cout << cat << '\n';

   // https://en.cppreference.com/w/cpp/language/range-for
   for (const auto& itr : cat) { std::cout << itr << ' '; }
   std::cout << '\n';

   // https://www.fluentcpp.com/2020/02/11/reverse-for-loops-in-cpp/
   for (const auto& itr : cat | std::views::reverse) { std::cout << itr << ' '; }
   std::cout << "\n\n";

   // range-based for loops work with regular arrays as well
   int arr[] { 5, 10, 15, 20, 25 };

   for (const auto& itr : arr) { std::cout << itr << ' '; }
   std::cout << '\n';

   for (const auto& itr : arr | std::views::reverse) { std::cout << itr << ' '; }
   std::cout << '\n';

   std::cout << "\nPi: " << std::numbers::pi << '\n';
}