Sphere store

#include <iostream>
#include <vector>
#include <cmath>
#include <cstdlib>

using namespace std;

const double PI = 3.141;

class Sphere
{
    public:
        Sphere();
        int menu();
        double calculateArea(int);
        double calculateVolume(int);
        double getRadius();
        void setRadius(double);
        void AddSphere();
        void sortSpheres();
        void DisplaySphere() const;

    private:
        double radius;
};

vector <Sphere> sphere(0);

Sphere::Sphere()
{
    radius = 0.0;
}

double Sphere::getRadius()
{
    return radius;
}

void Sphere::setRadius(double r)
{
    radius=r;
}

double Sphere::calculateArea(int i)
{
    Sphere s; //using Sphere class.
    return (4*PI*pow(radius, 2));
}

double Sphere::calculateVolume(int i)
{
    Sphere s;
    return ((4*PI*pow(radius, 3))/3);
}

void Sphere::AddSphere()
{
    Sphere s;
    double radius;
    cout << "Enter radius ";
    cin >> radius;
    while((radius < 0) || (cin.fail() !=0))
    {
        if(cin.fail() !=0)
        {
            cout << "Error! Can't read it! \n" << endl << "Please type it again.";
            cin.clear();
            cin.ignore(256,'\n');
        }
        else if(radius < 0)
        {
            cout << "Type value of postive" << endl; // between 1~4
        }
        cin >> radius;
    }
    s.setRadius(radius);
    sphere.push_back(s);
}


void Sphere::sortSpheres()
{
    Sphere temp;
    for (int a = 0; a < sphere.size(); a++)
    {
        for (int i = 0; i < sphere.size()-1; i++)
        {
            if (sphere[i].calculateVolume(i) > sphere[i+1].calculateVolume(i+1))
            {
                temp = sphere[i+1];
                sphere[i+1] = sphere[i];
                sphere[i] = temp;
            }
        }
    }
}

void Sphere::DisplaySphere() const
{
            Sphere s;
            cout << "All your Sphere: " << endl;
            for(int i =0; i<sphere.size(); i++)
            {
                cout << "Sphere: " << i+1 << endl << "Radius: " << sphere[i].getRadius() << endl;
                cout << "Volume: " << sphere[i].calculateVolume(i) << endl;
                cout << "Area: " << sphere[i].calculateArea(i) << endl << endl;
            }
}




int Sphere::menu()
{
    int choice;
        system("CLS"); //Flush the stream
        cout << "--Menu--" << endl << endl;
        cout << "1. Add spheres" << endl;
        cout << "2. Sort sphere" << endl;
        cout << "3. Displays all" << endl;
        cout << "4. Quit" << endl;
        cin >> choice;

    while((choice < 0 || choice > 4) || (cin.fail() !=0))
    {
        if(cin.fail() !=0)
        {
            cout << "Error! Can't read it! \n" << endl << "Please type it again in number(1~4).";
            cin.clear();
            cin.ignore(256,'\n');
        }
        else if(choice < 0 || choice > 4)
        {
            cout << "Between 1~4 please." << endl; // between 1~4
        }
        cout << "--Menu--" << endl << endl;
        cout << "1. Add spheres" << endl;
        cout << "2. Sort sphere" << endl;
        cout << "3. Displays all" << endl;
        cout << "4. Quit" << endl;
        cin >> choice;
    }
    return choice;
}


int main()
{
    Sphere s;
    int m;
    bool goOn = true;

    while(goOn==true)
    {
        m=s.menu();
        switch(m)
        {
            case 1:// Sphere
            {
                s.AddSphere();
                break;
            }
            case 2:// Sort sphere
            {
                s.sortSpheres();
                break;
            }
            case 3:// Displays all
            {
                s.DisplaySphere();
                system("pause");
                break;
            }
            case 4: //Quit, couldn't find any method, other than exit(0);
            {
                cout << "Thank you for using the program and See you later!";
                goOn = false;
                break;
            }
        }
    }
    return 0;
}