编译可以通过但是在输入数字之后就一直无法继续运行怎么回事？（一部分代码）class Point{ int x,y; public: void set(int a,int b) {x=a;y=b;} double getx() {return x;} double gety() {return y;}}; class PointArray{ Point a[3]; public: double getxx() {return a[2].getx()-a[0].getx();} double getyy() {return a[2].gety()-a[0].gety();} Point& get1() {return a[0]; } Point& get2() {return a[1]; } Point& get3() {return a[2]; }};class Polygon{ PointArray a; public: virtual double area()=0; void setVertices(int a1,int a2,int a3,int a4,int a5=0,int a6=0); double getlong() {return a.getxx();} double gethigh() {return a.getyy();}};void Polygon::setVertices(int a1,int a2,int a3,int a4,int a5,int a6){ a.get1().set(a1,a2); a.get2().set(a3,a4); a.get3().set(a5,a6);}class Rectangle:public Polygon{ public: double area() {return getlong()*gethigh();}};