enum
{
/* G, A, T, C, and N */

DNA_G,
DNA_A,
DNA_T,
DNA_C,
DNA_N

};

struct node {
	int DNA;	

	struct node *next;
};


struct node *new_node()
{
	struct node *node;

	r = malloc(struct node);
	if(!r)
		return NULL;

	r->next = NULL;

	return r;
}

struct node *link_node(struct node *list, struct node *node)
{
	for(;list->next;list=list->next);

	list->next=node;
}

int main()
{
	struct node *node1, *node2, *node3, *head;

	node1=new_node();
	node2=new_node();
	node3=new_node();

	head=node1;

	node1->DNA=DNA_C;
	node2->DNA=DNA_G;
	node3->DNA=DNA_C;

	link_node(head, node2);
	link_node(head, node3);

}