oop_object_factory

#include <iostream>
#include <string>

using namespace std;

class BadShapeCreation {
    string type;
public:
    BadShapeCreation(string type):type(type) {}
    string what() { return "Cannot create type " + type; }
};

class Shape {
public:
    virtual void draw() = 0;
    virtual void erase() = 0;
    virtual ostream& ins(ostream& os)const = 0;
    virtual ~Shape() {}
    static Shape* factory(const char* type) throw (BadShapeCreation);
};
ostream& operator<<(ostream& os, const Shape& obj) { return obj.ins(os); }

class Circle: public Shape {
    static int counter;
    int no;
    Circle() { no=++counter; }
    friend class Shape;
public:
    void draw() { cout <<"Circle "<< no <<" :draw\n"; }
    void erase() { cout <<"Circle "<< no <<" :erase\n"; }
    ~Circle() { cout <<"Circle "<< no <<" ~Circle\n"; }
    ostream& ins(ostream& os) const { return os <<"Circle "<< no; }
};
int Circle::counter=0;

class Triangle: public Shape {
    static int counter;
    int no;
    Triangle() { no=++counter; }
    friend class Shape;
public:
    void draw() { cout <<"Triangle "<< no <<" :draw\n"; }
    void erase() { cout <<"Triangle "<< no <<" :erase\n"; }
    ~Triangle() { cout <<"Triangle "<< no <<" ~Triangle\n"; }
    ostream& ins(ostream& os) const { return os<<"Triangle "<<no; }
};
int Triangle::counter=0;

class Square: public Shape {
    static int counter;
    int no;
    Square() { no=++counter; }
    friend Shape* getObjS();
public:
    void draw() { cout <<"Square "<< no <<" :draw\n"; }
    void erase() { cout <<"Square "<< no <<" :erase\n"; }
    ~Square() { cout <<"Square "<< no <<" ~Square\n"; }
    ostream& ins(ostream& os) const { return os<<"Square "<<no; }
};
int Square::counter=0;

Shape* getObjS() { return new Square; }

Shape* Shape::factory( const char* type ) throw (BadShapeCreation) {
    switch(type[0]) {
    case 'C': return new Circle;
    case 'T': return new Triangle;
    case 'S': return getObjS();
    default: throw BadShapeCreation(type);
    }
}

char * askForType() {
    char* s[] = { "Circle", "Square", "Triangle", "None" };
    return s[rand()%4];
}

int main() {
    Shape ** shapes;
    cout <<"Enter the number of objects: ";
    int n;
    cin >> n;
    shapes = new Shape *[n];

    for(int i=0; i<n; i++) {
        Shape * s;
        try {
            s = Shape::factory(askForType());
        } catch(BadShapeCreation e) {
            cout << e.what() << endl;
            i--;
            continue;
        }
        shapes[i] = s;
    }

    cout<<"\n The Objects Are:\n";
    for(int i=0; i<n; i++) {
        cout << i <<"   "<<*shapes[i]<<endl;
    }

    cout<<"\n Operating the objects:\n";
    for(int i=0; i<n; i++) {
        shapes[i]->draw();
        shapes[i]->erase();
    }

    cout<<"\n Purging the objects:\n";
    for(int i=0; i<n; i++) delete shapes[i];

    system("PAUSE");
    return 0;
}