MovingAverage.h

#include <deque>
template<class InputType, class InnerAvgType=double,
	class AvgType=InputType>
class MovingAverage {
	int average_count;
	std::deque<InputType> buffer;
	InnerAvgType average;
public:
	MovingAverage() : average_count(1), average(0) { }
	MovingAverage(int average_count)
		: average_count(average_count), average(0)
	{
		assert(average_count > 0);
	}
	
	int getAverageCount() const {
		return average_count;	
	}
	void setAverageCount(int n) {
		assert(n > 0);
		average_count = n;
		reset();
	}
	
	// reset average value and counter.
	void reset() {
		average = 0;
		buffer.clear();
	}
	// average value stability
	bool isStable() const {
		return buffer.size() >= average_count;
	} 
	// update and return average value
	AvgType update(const InputType& input) {
		InnerAvgType total = average * buffer.size();
		if(buffer.size() >= average_count) {
			total -= buffer.at(0);
			buffer.pop_front();
		}
		buffer.push_back(input);
		total += (InnerAvgType)input;
		average = total / buffer.size();
		return (AvgType)average;
	}
	operator AvgType () {
		return (AvgType)average;
	}
};

test.cpp

#include <iostream>
#include <assert.h>
#include "MovingAverage.h"
int main(int argc, char*argv[]) {
	MovingAverage<int> intAverager(5);
	int data[]		= {
		1,2,3,4,5,6,7,8,9,10,9,8,7,
		6,5,4,3,2,1,0,0,0,0,0,0,0};
	for(int i = 0; i < sizeof(data)/sizeof(data[0]); i++) {
		int average = intAverager.update(data[i]);
		std::cerr << "input " << data[i]
			<< " average = " << average << std::endl;
	}
}