main()中Student stud1(1001);的错误在哪#include <iostream>#include <string>using namespace std;class Student{public: Student(int n,){num=n; }virtual void display()=0; protected: int num;};class Graduate:public Student{public: Graduate(int n,float p):Student(n),pay(p){} void display( ){ cout<<num<<pay<<endl;} private: float pay;};int main(){ Student stud1(1001); Graduate grad1(2001,563.5); Student *pt; pt=&grad1; pt->display(); return 0;