如何在主函数中创建对象？

Question

#include<iostream>
using namespace std;

class distance    //class
{
private:
    int feet;
    float inches;
public:
    distance() :feet(0), inches(0.0)  //constructor
    {}
    distance(int ft, float in) :feet(ft), inches(in)  //constructor
    {}
    void getdist()  //get values
    {
        cout << "Enter feet :";
        cin >> feet;
        cout << "Enter inches :";
        cin >> inches;
    }
    void showdist() //show values
    {
        cout << feet << "-" << inches << endl;
    }
    void adddist(distance, distance); //add distance through objects 
};

void distance::adddist(distance d2, distance d3) //add distance
{
    inches = d2.inches + d3.inches;
    feet = 0;
    if (inches >= 12.0)
    {
        inches -= 12.0;
        feet++;
    }
    feet += d2.feet + d3.feet;
}

int main()
{

}

我正在为家庭作业写几个课程，我希望我的班级成员函数不可能在main中调用。如果是，我希望程序退出。我如何知道何时调用我的成员函数？