运行下列代码，屏幕上输出（ ）。

#include <iostream>

using namespace std;

class shape {

protected:

int width, height;

public:

shape(int a = 0, int b = 0) {

width = a;

height = b;

}

virtual int area() {

cout << "parent class area: " <<endl;

return 0;

}

};

class rectangle: public shape {

public:

rectangle(int a = 0, int b = 0) : shape(a, b) { }

int area () {

cout << "rectangle area: ";

return (width * height);

}

};

class triangle: public shape {

public:

triangle(int a = 0, int b = 0) : shape(a, b) { }

int area () {

cout << "triangle area: ";

return (width * height / 2);

}

};

int main() {

shape *pshape;

rectangle rec(10, 7);

triangle tri(10, 5);

pshape = &rec;

pshape->area();

pshape = &tri;

pshape->area();

return 0;

}