#include <iostream>
#include <cmath>
#include <random>
#include <fstream>

class MonteCarlo{
public:
    MonteCarlo(double begin,
            double end,
            size_t number,
            std::function<double(double)> function,
            std::function<double(double)> antiderivative) :
            begin_(begin), end_(end), number_(number),
            function_(function), antiderivative_(antiderivative), result_(0) {}


    void Calculate() {
      std::random_device rd;
      std::mt19937 gen(rd());
      std::uniform_real_distribution<> dis(begin_, end_);

      for (size_t i = 0; i < number_; ++i) {
        result_ += function_(dis(gen));
      }


      result_ *= (end_ - begin_)/number_;
      true_result_ = antiderivative_(end_) - antiderivative_(begin_);
      difference_ = fabs(true_result_ - result_);
    }

    double GetResult() {
      if (!calculated_) {
        Calculate();
        calculated_ = true;
      }

      return result_;
    }

    double GetDiff() {
      if (!calculated_) {
        Calculate();
        calculated_ = true;
      }

      return difference_;
    }

    double GetTrueResult() {
      if (!calculated_) {
        Calculate();
        calculated_ = true;
      }

      return true_result_;
    }

private:
    double begin_;
    double end_;
    size_t number_;
    std::function<double(double)> function_;
    std::function<double(double)> antiderivative_;

    bool calculated_;

    double result_;
    double true_result_;
    double difference_;
};


double func(double x) {
  return cos(x);
}

double antiderivative(double x) {
  return sin(x);
}


int main() {
  auto file_name = "result.txt";
  std::ofstream file;
  file.open(file_name);
  for (int exp_num = 1; exp_num < 100; ++exp_num) {
    auto MCcalc = MonteCarlo(
            /* начало = У*/ 0,
            /* конец = */ 3,
            /* количество точек = */ 10000,
            /* функция = */ func,
            /* первообразная = */ antiderivative);

    MCcalc.Calculate();
    file << exp_num << ' ' << MCcalc.GetDiff() << std::endl;
  }

  file.close();
  return 0;
}