チェーンテーブルの追加削除(補足待ち...)

#include 
using namespace std;
struct mylist* GetList();
struct node* GetNode(int n);
void PrintList(struct mylist* L);
void InsertNode(struct mylist* L, int n);
void DeleteNode(struct mylist* L, int n);
void SelectionSort(struct mylist* L, int n);

struct mylist {
     //   
	struct node* head;
	struct node* tail;
	int size;
};

struct node {
     //  
	int data;
	struct node* next;
	struct node* prev;
};

int main()
{
     
	struct mylist* L = GetList();
	int i, val;
	for (i = 0; i < 5; i++) {
     
		cout << "input a num:" << endl;
		cin >> val;
		InsertNode(L, val);
		PrintList(L);
	}

	cout << "input a num for insertion:" << endl;
	cin >> val;
	InsertNode(L, val);
	PrintList(L);

	cout << "input a num for deletion:" << endl;
	cin >> val;
	DeleteNode(L, val);
	PrintList(L);

	cout << "After sorting:" << endl;
	SelectionSort(L,val);
	PrintList(L);
	return 0;
}

struct mylist* GetList() {
     
	struct mylist* L = new struct mylist;
	L->head = GetNode(0);
	L->tail = GetNode(0);
	L->head->next = L->tail;
	L->tail->prev = L->head;
	L->size = 0;
	return L;
}

struct node* GetNode(int n) {
     
	struct node* pnode = new struct node;//(struct node*)malloc(sizeof(struct node))
	pnode->data = n;
	pnode->next = NULL;
	pnode->prev = NULL;
	return pnode;
}

void InsertNode(struct mylist* L, int n) {
     //  
	struct node* p = L->head->next;//      p， p          
	while (p != L->tail) {
     
			struct node* newNode = GetNode(n);
			newNode->next = p;//p        
			newNode->prev = p->prev;//p-prev        

			/*          ，     p->prev       */

			p->prev->next = newNode;//     p-prev   
			p->prev = newNode;//     p   
			L->size++;
			return;
	}
	/*   p   L->tail */
	struct node* newNode = GetNode(n);
	newNode->next = p;
	newNode->prev = p->prev;
	p->prev->next = newNode;
	p->prev = newNode;
	L->size++;
	return;
}

void PrintList(struct mylist* L) {
     
	struct node* p = L->head->next;
	while (p != L->tail) {
     
		cout << p->data << "  ";
		p = p->next;
	}
	cout << endl;
}

void DeleteNode(struct mylist* L, int n) {
     
	struct node* p = L->head->next;
	while (p != L->tail) {
     
		if (n == p->data) {
     
			p->prev->next = p->next;
			p->next->prev = p->prev;
			delete p; //free(p)
			L->size--;
			return;
		}
		p = p->next;
	}
	cout << "the number does not exist" << endl;
}

void SelectionSort(struct mylist* L, int val)
{
     
	struct node* p = NULL;
	struct node* q = NULL;
	for (p = L->head->next; p != L->tail; p = p->next) {
     
		for (q = p->next; q != L->tail; q = q->next) {
     
			if (p->data > q->data) {
     
				int tmp = q->data;
				q->data = p->data;
				p->data = tmp;
			}
		}
	}
}