calculates the standard devation and variances of the given data set and determines whether a number is an outlier in the set

#include <iostream>
#include <cstdarg>
#include <vector>
#include <cmath>

using namespace std;

struct sd
{
    sd();
    sd(int,...);
    ~sd(){s.clear();}
    public:
        int t;
        vector<double> s;
        double sum;
        double var(){
            double avg = mean(),to = 0;
            for(vector<double>::iterator start = s.begin();start<s.end();start++)
                to += pow(avg - *start,2);
            return to/t;
        }
        double mean(){return (sum/t);}
        double std(){return sqrt(var());}
        bool isOutlier(double x){
            double s = std()*3,avg = mean();
            return (x>(avg-s)&&x<(avg+s)?true:false);
        };
};

sd::sd()
{
    int c;
    double x;
    sum = 0;
    cout << "Enter number of data sets: ";
    cin >> t;
    if(!cin)
        cerr << "You must enter an integer!";
    else
    {
        vector<double> m(t);
        c = t;
        cout << "Enter data sets:\n";
        do
        {
            cin >> x;
            m[t-c] = x;
            sum+=x;
        }   while(--c>0);
        s = m;
        m.clear();
    }
}

sd::sd(int h,...)
{
    sum = 0;
    va_list vl;
    va_start(vl,h);
    double val;
    t = h;
    vector<double> m(h);
    for (int i=0;i<h;i++)
    {
        m[i] = double(val=va_arg(vl,double));
        sum+=val;
    }
    s = m;
    m.clear();
    va_end(vl);
}

int main()
{
    sd test(5,600.0, 470.0, 170.0, 430.0, 300.0);

    cout << test.var() << endl;     // returns variance
    cout << test.std() << endl;     // returns standard deviation
    cout << test.isOutlier(450.0);  // returns true if 450 is an outlier

    return 0;
}