Cumulative Average

average.cpp

#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <cstdio>
#include <iterator>

using namespace std;

template<int begin, int end>
class Rand {
public:
    Rand() {
        srand( time(0) );
    }

    int operator()() const {
        return (rand()%(end - begin) + begin);
    }
};

template <typename TypeOut>
class AverageCalculator
{
public:
    AverageCalculator()
        : counter_()
        , avg_()
    {}

    template <typename TypeIn>
    void operator()(const TypeIn& v) {
        ++counter_;

        avg_ = avg_ + (1.f/counter_)*(v - avg_);
    }

    TypeOut average() const {
        return static_cast<TypeOut>(avg_);
    }

private:
    size_t counter_;
    double avg_;
};


int main()
{
    std::vector<int> v(10);
    std::generate(v.begin(), v.end(), Rand<0,10>());

    std::copy(v.begin(), v.end(),
              std::ostream_iterator<int>(cout, " "));

    std::cout << std::for_each(v.begin(), v.end(), AverageCalculator<double>()).average()
                 << std::endl;


    return 0;
}