Making Priority Queue of Objects - c++

Question

I have error in line 7 that missing ; before * I want to make Priority Queue of Objects which gets priority by Student ID and also it is not necessary to have object pointer it can be object itself
#include<iostream>
#include<string>
using namespace std;
struct node
{
int priority;
Student * S;
node * next;
};
class Student
{
int ID;
string name;
public:
Student()
{
cin>>ID;
cin>>name;
}
void out()
{
cout<<"ID is : "<<ID<<" "<<"Name is : "<<name<<endl;
}
};
class Priority_Queue
{
node * head;
//node * back;
public:
Priority_Queue()
{
head=NULL;
//back=NULL;
}
void push(Student * Q, int a)
{
node * p=new node;
p->next=NULL;
p->priority=a;
p->S=Q;
if(head==NULL)
head=p;
else
{
node * q=head;
node * r=NULL;
while(a<=q->priority)
{
r=q;
q=q->next;
}
r->next=p;
p->next=q;
}
}
Student * pop()
{
if(isempty())
{
cout<<"Empty"<<endl;
exit(1);
}
else
{
return head->S;
head =head->next;
}
}
bool isempty()
{
if(head==NULL)
return true;
else return false;
}
};
int main()
{
Student S1,S2,S3,S4;
return 0;
}
Errors in my Code
1>d:\codes\priority queue\priority queue\1.cpp(7): error C2143: syntax error : missing ';' before '*'
1>d:\codes\priority queue\priority queue\1.cpp(7): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>d:\codes\priority queue\priority queue\1.cpp(7): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>d:\codes\priority queue\priority queue\1.cpp(41): error C2039: 'S' : is not a member of 'node'
1> d:\codes\priority queue\priority queue\1.cpp(5) : see declaration of 'node'
1>d:\codes\priority queue\priority queue\1.cpp(66): error C2039: 'S' : is not a member of 'node'
1> d:\codes\priority queue\priority queue\1.cpp(5) : see declaration of 'node'

Answer 1

Actually the problem is, that the struct node does not know about the class student, as it is defined after. A workaround is to declare Student before node, but you could aswell put Student in an extra header and include that header in the node header (personally I'd prefer that way.).
class Student;
struct node
{
int priority;
Student * S;
node * next;
};

Answer 2

You should use forward declaration:
struct node;
class Student;
struct node
{
int priority;
Student * S;
node * next;
};
// . . .