设计一个抽象类Shape。在此基础上派生出类Triangle和Circle，两者都有计算对象面积的函数GetArea和计算对象周长的函数GetPerim。编写程序测试。

以下是实现代码：

#include <iostream>
using namespace std;

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

class Triangle : public Shape {
private:
    double a, b, c;
public:
    Triangle(double _a, double _b, double _c) : a(_a), b(_b), c(_c) {}
    double GetArea() {
        double s = (a + b + c) / 2;
        return sqrt(s * (s - a) * (s - b) * (s - c));
    }
    double GetPerim() {
        return a + b + c;
    }
};

class Circle : public Shape {
private:
    double r;
public:
    Circle(double _r) : r(_r) {}
    double GetArea() {
        return 3.1415926 * r * r;
    }
    double GetPerim() {
        return 2 * 3.1415926 * r;
    }
};

int main() {
    Shape* p[2];
    p[0] = new Triangle(3, 4, 5);
    p[1] = new Circle(2);
    for (int i = 0; i < 2; ++i) {
        cout << "Area: " << p[i]->GetArea() << endl;
        cout << "Perim: " << p[i]->GetPerim() << endl;
    }
    return 0;
}

输出结果为：

Area: 6
Perim: 12
Area: 12.5664
Perim: 12.5664