大神帮我看看，我不会用函数啊，而且这提示说的也不懂，既然是全局函数，要派生有什么用？

Question

已知一个全局函数printArea(arg),其中，arg为某一种平面图形，该函数的作用是打印参数arg所表示图形的面积。先假设，只存在正方形、圆形、正三角形三种平面图形。使用继承的方式，设计相关的类，并实现该全局函数的功能。
提示：设计基类Shape，设计派生类Square，Circle，Triangle

Answer 1

这是代码有不适当的地方请大家提出来，谢谢
#include
#include
using namespace std;

class Shape
{
public:
virtual double area() = 0;
};

class Circle :public Shape
{
public:
Circle(int radius){
this->radius = radius;
}
virtual double area(){
return 3.14*radius*radius;
}
private:
int radius;
};
class Square :public Shape
{
public:
Square(int rim){
this->rim = rim;
}
virtual double area(){
return rim*rim;
}
private:
int rim;
};

class Triangl :public Shape
{
public:
Triangl(double rim){
this->rim = rim;
}
virtual double area(){
double i = rim*rim;
double j = (rim/2)*(rim/2);
double hige = sqrt(i - j);
return rim*hige/2;
}
private:
double rim;
};

void printArea(Shape *arg)
{
cout << arg->area() << endl;
}

int main(int argc, char* argv[])
{
Shape *squ = new Square(2);
Shape *cir = new Circle(2);
Shape *tri = new Triangl(5);

printArea(squ);
printArea(cir);
printArea(tri);

delete squ;
delete cir;
delete tri;

return 0;

}