hỏi về code class bị sai

#include<iostream>
using namespace std;
class node;
class queue;
//
class data
{
	int a;
	public:
	int geta(){
		return a;
	}
	void nhapdata(data *x);
	friend class node;
	friend void inserttail(queue *q, data x);
	friend class queue;
	friend void pop(queue *q);
};
//
void data::nhapdata(data *x)
{
	cout<<"nhap data (o day la kieu int)";
	cin>>x->a;
}
class node
{
	data infor;
	node *link;
	public:
	friend void inserttail(queue *q, data x);	
	friend class queue;
	friend void pop(queue *q);		
};
//
class queue
{
	node *head;
	node *tail;
	int spt;// lỗi ở đây
	public:
	friend void inserttail(queue *q,data x);// them cuoi
	void init(queue *q);
	int empty(queue q);
	void fifo(queue *q);
	void trave(queue q);
	friend void pop(queue *q);// xoa dau
};
//
void queue::init(queue *q)
{
	q->head=NULL;
	q->tail=NULL;
	q->spt=0;
}
//
int empty(queue q)
{
	return(q.spt==0);//spt = 0 thi rong
}
//
void pop(queue *q)// xoa dau
{
	if (empty(*q)) cout<<"queue rong khong xoa dc";
	else{
		data x= q->head->infor;
		if(q->spt==1) init(q);
		else
		{
		q->head=q->head->link;
		q->spt--;
		cout<<"da xoa pt dau tien la "<<x.a;
	}
}
}
void inserttail(queue *q, data x)
{
	node *p;
	p=(node*)malloc(sizeof(node));
	p->infor=x;
	p->link=NULL;
	if(empty(*q))
	{
		q->head=p;
		q->tail=p;
	}
	else{
		q->tail->link=p;
		q->tail=p;
	}
	++q->spt;
}	
void queue::travel(queue q)
{
	node *p=q.head;
	while(p!=NULL){
	cout<<p->infor.geta()<< " ";
	p=p->link;
}}
void queue::fifo(queue *q)
{
	data x;
	init(q);
	do{
		x.nhapdata(&x);
		if(x.geta()!=0)
		inserttail(q,x);
	}
	while(x.geta!=0);
}	

nó bị lỗi cái số phần tử… em chẳng hiểu nó là ntn luôn…