下列程序的执行结果是______。
#include＜iostream.h＞
class Student

public:
Student(int xx)x=xx;
virtual float calcTuition( );
protected:
int x;
;
float Studertt::calcTuition( )

return float(x*x);

class GraduateStudent:public Student

public:
GraduateStudent(int xx):Student(xx)
float calcTuition( );
;
float Graduatestudent::calcTuition( )

return float(x*2);

void main( )

Student s(20);
GraduateStudent gs(30);
cout＜＜s.calcTuition( )＜＜" "＜＜gs.calcTuition( )＜＜endl;
//计算学生s和研究生gs的学费