1.定义circle类 2.在main中定义circle对象数组 3.在main中定义circle对象指针，指向已有的对象 4.在main中定义circle对象指针，使用new和delete分配和释放内存

1. 定义Circle类

class Circle {
private:
    double radius;
public:
    Circle(double r) {
        radius = r;
    }
    double area() {
        return 3.14 * radius * radius;
    }
};

2. 在main中定义Circle对象数组

int main() {
    Circle circles[3] = { Circle(1.0), Circle(2.0), Circle(3.0) };
    for(int i = 0; i < 3; i++) {
        cout << "Circle " << i+1 << " area: " << circles[i].area() << endl;
    }
    return 0;
}

3. 在main中定义Circle对象指针，指向已有的对象

int main() {
    Circle c1(4.0);
    Circle *p = &c1;
    cout << "Circle area using pointer: " << p->area() << endl;
    return 0;
}

4. 在main中定义Circle对象指针，使用new和delete分配和释放内存

int main() {
    Circle *p = new Circle(5.0);
    cout << "Circle area using dynamic allocation: " << p->area() << endl;
    delete p;
    return 0;
}