若有以下程序: #include <iostream> using namespace std; #define PI 3.14 class Point { private: int x,y; public: Point (int a,int b){x=a;y=b; } int getx () {return x; } int gety() {return y; } }; class Circle : public Point { int r; public: Circle(int’ a, int b,int C) : Point (a, b){r=c; } int getr() {return r; } double area() {return PI*r*r; } }; int main() { Circle c1(5,7,10); cout<<c1.area()<<end1; return 0; } 程序执行后的输出结果是 【15】 。