//
// C++ class to compute mean, variance and standard deviation
//

class Stats {
public:
    Stats() {
	sum = 0;
	sumsq = 0;
	nn = 0;
    }

    void datum(double v) {
	sum += v;
	sumsq += v * v;
	nn += 1;
    }

    double mean() {
	return(sum / nn);
    }

    double variance() {
	return( (sumsq - (sum * sum) / nn) / (nn - 1) );
    }

    double stdev() {
	return( sqrt(variance()) );
    }

    int n() {
	return(nn);
    }

    double sum, sumsq;
    int nn;
};