Lỗi C4700: uninitialized local variable 'p' used ai giúp mình với

#include "stdafx.h"
#include "conio.h"
#include "iostream"
#include "stdio.h"


struct SinhVien
{
	char strMSSV[9];
	char strHoTen[30];
	char strNamSinh[5];
	float fDiemTrungBinh;
};

struct SinhVienNode
{
	SinhVien info;
	SinhVienNode * pNext;
};

struct List
{
	SinhVienNode * pHead;
	SinhVienNode * pTail;
};

void XuatDanhSach(SinhVienNode * p);
void init(List & L);
SinhVienNode * getNode(char MSSV[9], char HoTen[30], char NamSinh[5], float DiemTrungBinh);
void addFirst(List & l, SinhVienNode * p);
void addTail(List & l, SinhVienNode * p);
SinhVienNode * insertHead (List & l, char MSSV[9], char HoTen[30], char NamSinh[5], float DiemTrungBinh);
SinhVienNode * insertTail (List & l, char MSSV[9], char HoTen[30], char NamSinh[5], float DiemTrungBinh);
void addAfter(List & l, SinhVienNode * q, SinhVienNode *p);

void main()
{
	List lop18TH01;
	int a, b;
	init(lop18TH01);
	do
	{
	printf("Nhap so luong sinh vien muon them: ");
	scanf_s("%d", &a);
	}
	while (a < 1);
printf("
");

SinhVienNode * p;
	char strMSSV[9];
	char strHoTen[30];
	char strNamSinh[5];
	float fDiemTrungBinh;
	for (int i=1; i<=a; i++)
	{
		printf("Sinh vien thu %d:", i);
		printf("Nhap vao MSSV: ");
		scanf_s("%s", &p->info.strMSSV);
		printf("Nhap vao ho va ten: ");
		scanf_s("%s", &p->info.strHoTen);
		printf("Nhap vao nam sinh: ");
		scanf_s("%s", &p->info.strNamSinh);
		printf("Nhap vao diem trung binh: ");
		scanf_s("%f", &p->info.fDiemTrungBinh);
		p = getNode(strMSSV, strHoTen, strNamSinh, fDiemTrungBinh);
		addTail(lop18TH01, p);
	}
/*
	_getch();
	system("cls");
	do
	{
		printf("1 	
");
		printf("2 	
");
		printf("3 	
");
		printf("4 	
");
		printf("5 	
");
		printf("0 	
");
		printf("Chon: ");
		scanf_s("%d", &b);
		system("cls");
		switch (b)
		{
			case 1:
				break;
			case 2:
				_getch(); break;
			case 3:
				_getch(); break;
			case 4:
				_getch(); break;
			case 5:
				_getch(); break;
		};
		system("cls");
	}
	while (a != 0);
*/
	_getch();
}

void XuatDanhSach(SinhVienNode * p)
{
	printf("%s - %s - %s - %.1f
", p->info.strMSSV, p->info.strHoTen, p->info.strNamSinh, p->info.fDiemTrungBinh);
}

void init(List & l)
{
	l.pHead = l.pTail = NULL;
}

SinhVienNode * getNode(char MSSV[9], char HoTen[30], char NamSinh[5], float DiemTrungBinh)
{	
	SinhVienNode * p = new SinhVienNode;
	if (p == NULL)
		return NULL;
	strcpy_s (p->info.strMSSV, MSSV);
	strcpy_s (p->info.strHoTen, HoTen);
	strcpy_s (p->info.strNamSinh, NamSinh);
	p->info.fDiemTrungBinh = DiemTrungBinh;
	p->pNext = NULL;
	return p;
}

void addFirst(List & l, SinhVienNode * p)
{
	if (l.pHead == NULL)
		l.pHead = l.pTail = p;
	else{
		p->pNext = l.pHead;
		l.pHead = p;
	}
}


void addTail(List & l, SinhVienNode * p)
{
	if (l.pHead == NULL)
		l.pHead = l.pTail = p;
	else
	{
		l.pTail->pNext = p;
		l.pTail = p;
	}
}

SinhVienNode* insertHead(List & l, char MSSV[9], char HoTen[30], char NamSinh[5], float DiemTrungBinh)
{
	SinhVienNode * p = getNode (MSSV, HoTen, NamSinh, DiemTrungBinh);
	if (p != NULL)
	{
		addFirst (l, p);
		return p;
	}
	return NULL;
}

SinhVienNode * insertTail (List & l, char MSSV[9], char HoTen[30], char NamSinh[5], float DiemTrungBinh)
{
	SinhVienNode * p = getNode (MSSV, HoTen, NamSinh, DiemTrungBinh);
	if (p != NULL)
	{	
		addTail (l, p);
		return p;
	}
	return p;
}
	
void addAfter(List & l, SinhVienNode * q, SinhVienNode *p)
{
	if (q != NULL)
	{	
		p->pNext = q->pNext;
		q->pNext = p;
	}
	if (q = l.pTail)
		l.pTail = p;
	addFirst(l, p);
}