quiz: Polymorphism & qsort

深入理解指针

CShape *pShapes[MAX];//指针数组 ATTATION 

#include <iostream>

#include <cmath>

using namespace std;

class CShape{

public:

virtual double area(){

return 0;

}

virtual void PrintArea(){}

};

class CTriangle:public CShape{

public:

int a;

int b;

int c;

virtual double area(){

double p = (a + b + c)*0.5;

return sqrt(p*(p - a)*(p - b)*(p - c));

}

void PrintArea(){

cout << "Triangle:" << area() << endl;

}

};

class CRectangle :public CShape{

public:

int width;

int height;

virtual double area(){

return width*height;

}

void PrintArea(){

cout << "Rectangle:" << area()<< endl;

}

};

class CCircle :public CShape{

public:

int r;

const double pi = 3.14;

virtual double area(){

return pi*r*r;

}

void PrintArea(){

cout << "Circle:" << area() << endl;

}

};

#define MAX  100

int MyCompare(const void *ele1_,const void *ele2_){

CShape **p1, **p2;

p1 = (CShape **)ele1_;

p2 = (CShape **)ele2_;

double a1, a2;

int tmp;

a1 = (*p1)->area();

a2 = (*p2)->area();

if (a1 < a2)

tmp = -1;

else if (a1 > a2)

tmp = 1;

else

tmp = 0;

return tmp;

}

int main(){

int n;

CRectangle *pr;

CCircle *pc;

CTriangle *pt;

CShape *pShapes[MAX];

cin >> n;

for (int i = 0; i < n; i++){

char c;

cin >> c;

switch (c){

case 'R':

pr = new CRectangle();

cin >> pr->height >> pr->width;

pShapes[i] = pr;

break;

case 'T':

pt = new CTriangle();

cin >> pt->a >> pt->b >> pt->c;

pShapes[i] = pt;

break;

case 'C':

pc = new CCircle();

cin >> pc->r;

pShapes[i] = pc;

break;

}

}

qsort(pShapes, n, sizeof(CShape*), MyCompare);

for (int i = 0; i < n; i++)

pShapes[i]->PrintArea();

return 0;

}