class와 OOP 예제3 virtual function

#include <iostream> 

using namespace std;

class Shape {

protected:

int width, height;

public:

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

width = a;

height = b;

}

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 class area :" << endl;

return (width * height);

}

};

class Triangle : public Shape{

public:

Triangle(int a = 0, int b = 0) :Shape(a, b) { }

int area() {

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

return (width * height / 2);

}

};

// Main function for the program

int main() {

Shape *shape;

Rectangle rec(10, 7);

Triangle  tri(10, 5);

// store the address of Rectangle

shape = &rec;

// call rectangle area.

shape->area();

// store the address of Triangle

shape = &tri;

// call triangle area.

shape->area();

return 0;

}

--------------------------------------------

#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 class area :" << endl;

return (width * height);

}

};

class Triangle : public Shape{

public:

Triangle(int a = 0, int b = 0) :Shape(a, b) { }

int area() {

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

return (width * height / 2);

}

};

// Main function for the program

int main() {

Shape *shape;

Rectangle rec(10, 7);

Triangle  tri(10, 5);

// store the address of Rectangle

shape = &rec;

// call rectangle area.

shape->area();

// store the address of Triangle

shape = &tri;

// call triangle area.

shape->area();

return 0;

}