Link list segmentation fault

[iamtheone]

I'm writing a simple link list program, but got stuck. The first insert is working fine, the second one is giving a segmentation fault. Help me figure out the error. Here is my code:

#include<iostream>

using namespace std;

struct node{
	int data;
	node *next;
};
	
void insert(int num, node *&p);
void addAsFirst(int num, node *p);
int deleteNode(int num, int pos, node *p);
void print(node *&p);

int main(){
	node *p;
	p = NULL;
	insert(5, p);
	insert(8, p);
	insert(6, p);
	print(p);
	return 0;
}

void insert(int n, node *&p){
	node *q, *r;
	if (p==NULL){
		p = new node;
		p->data = n;
		p->next = NULL;
		cout<<"p: "<<p->data<<endl;
	}
	else{
		q = p;

		while(!q->next){
			cout<<"q: "<<q->data<<endl;
			q = q->next;
		}
		r = new node;
		r->data = n;
		r->next = NULL;
		q->next = r;
	}
}

void print(node *&p){
	node *q;
	if(p == NULL){
		cout<<"Link list is empty\n";
	}
	else{
		q = p;
		while(q != NULL){
			cout<<q->data<<" \t";
			q = q->next;
		}
	}
}