fejl i kode! :(

når jeg skriver følgende kode kommer den med denne fejl(8 gange):

must #include <typeinfo> before using typeid

koden:

#include <iostream>
#include <cstdlib>
using namespace std;

class figure {
    protected:
        double x, y;
    public:
        figure(double i, double j) {
            x = i;
            y = j;
        }
        virtual double area() = 0;
};

class triangle : public figure {
    public:
        triangle(double i, double j) : figure(i, j) {}
        double area() {
            return x * 0.5 * y;
        }
};

class rectangle : public figure {
    public:
        rectangle(double i, double j) : figure(i, j) {}
        double area() {
            return x * y;
        }
};

class circle : public figure {
    public:
        circle(double i, double j=0) : figure(i, j) {}
        double area() {
            return 3.14 * x * y;
        }
};

figure *factory()
{
    switch(rand() % 3 ) {
        case 0: return new circle(10.0);
        case 1: return new triangle(10.1, 5.3);
        case 2: return new rectangle(4.3, 5.7);
    }
    return 0;
}

int main()
{
    figure *p;
    int i;

    int t=0, r=0, c=0;

    for(i=0; i<10; i++) {
        p = factory();

        cout << "Objekt: " << typeid(*p).name();
        cout << ".  ";

        if(typeid(*p) == typeid(triangle)) t++;
        if(typeid(*p) == typeid(rectangle)) r++;
        if(typeid(*p) == typeid(circle)) c++;

        cout << "Areal " << p->area() << endl;
    }
    cout << endl;
    cout << "Objekter:\n";
    cout << "  Trekanter: " << t << endl;
    cout << "  Rektangler: " << r << endl;
    cout << "  Cirkler: " << c << endl;

    return 0;
}