void Course::Addstudent(Student& s){
	Node* p=new Node;
	p->Studentname=s.Getname();
	p->grade=0;
	p->next=studentlist;
	studentlist=p;
}
void Course::Setgrade(Student& s,float a){
	int i;
	Node* p;p=studentlist;
	for(i=0;i<studentnum;i++){
		if(strcmp(s.Getname(),p->Studentname)==0){
			p->grade=a;
		cout<<"scessfully"<<endl;
		exit(0);
		}
	}
}
float Course::Getstudentgrade(Student& s){
	int i;
	Node* p;p=studentlist;
	for(i=0;i<studentnum;i++){
		if(strcmp(s.Getname(),p->Studentname)==0)
			return p->grade;
		p=p->next;
	}
	cout<<"can't find student"<<endl;
	return 0;
}