c-resources/CPlusPlus20ForProgrammers-master/examples/ch06/histogram.cpp

// fig06_07.cpp
// Die-rolling program using an array instead of switch.
//#include <format> // C++20: This will be #include <format>
#include <iostream>
#include <array>
#include <random>

template <int N>
void accumulate(std::array<double, N>& histogram, double val, double lower, double upper){

	double del {(upper-lower)/N};
	for (int i{0}; i < N; i++){
		if ( val > i*del && val < (i+1) * del )
			histogram[i]++;
	}
	return;
}

int main() {
   // set up random-number generation
   std::random_device rd; // used to seed the default_random_engine
   std::default_random_engine engine{rd()}; // rd() produces a seed 

   double upper_bound = 1;
   double lower_bound = 0;
   std::uniform_real_distribution<double> randomReal{lower_bound, upper_bound};

   constexpr size_t N{4};
   double del {(upper_bound-lower_bound)/N};
   std::array<double, N> histogram{};

   // roll die 60,000 times; use die value as frequency index
   for (int roll{1}; roll <= 6000; ++roll) {
	   double val{ randomReal(engine)};
	   accumulate<N>(histogram, val, lower_bound, upper_bound);
   }


   std::cout <<  " Histogram : \n";

   // output each array element's value
   for (size_t face{1}; face < histogram.size(); ++face) {
      std::cout <<"Number of samples between " << lower_bound+face*del << " and " << lower_bound+(face+1)*del << " is " << histogram.at(face) << "\n";
   }
}

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