我用链表进行插入语删除操作后，发生了越界，我的代码哪里错了吗？

Question

#include
#include
#include
#include
#include
typedef struct Student{
char num[10]; //学号
char name[10]; //姓名
char gender[2]; //性别
int age; //年龄
}Student;

//链表的定义
typedef struct LNode{
Student* data; //存放学生信息的数据域
struct LNode *next; //指向下一个学生信息的指针域
}LNode,*linklist;

void input(int n, LNode **head){
if(n <= 0){
printf("输入错误\n");
return;
}
LNode p = *head = (LNode)malloc(sizeof(LNode));
int i;

for(i = 0; i < n; i++){
p->next=(LNode*)malloc(sizeof(LNode));
p->next->data = (Student*) malloc (sizeof(Student));
p->next->next = NULL;
scanf("%s %s %s %d",p->next->data->num, p->next->data->name, p->next->data->gender, &p->next->data->age);
p = p->next;
}
return;
}

//输出学生信息
void output(LNode p){
p=p->next;
while(p!= NULL){
printf("%s %s %s %d\n",p->data->num, p->data->name, p->data->gender, p->data->age);
p = p->next;
}
printf("\n");
}
//插入信息
void add(LNode *head, int n){
if(n<1){
printf("输入过小\n");
return;
}
LNode *p = (LNode)malloc(sizeof(LNode));
p->next = NULL;
scanf("%s %s %s %d",p->data->num, p->data->name, p->data->gender, &p->data->age);
int i = 1;
while(head!=NULL){
if(i == n){
p->next = head->next;
head->next = p;
break;
}
head = head->next;
i++;
}
if(head==NULL){
head->next = p;
}
}
//链表的删除
int del(LNode head, int n,int sum){
if(n printf("输入过小\n");
return -1;
}
if(n>sum){
printf("输入过大\n");
return -1;
}
linklist p;
p = (LNode)malloc(sizeof(LNode));
int i = 1;
while(i<=n-1) {
head=head->next;
i++;
}
p=head->next;
head->next=head->next->next;
free(p);
return 1;
}

int main(void){
LNode *head = NULL;
printf("请输入学生人数：");
int sum;
scanf("%d",&sum);
printf("请依次输入学号，姓名，性别，年龄：\n");
input(sum,&head);
output(head);

printf("请输入插入位置：");
int a;
scanf("%d",&a);
add(head,a);
sum++;
output(head);

printf("请输入删除位置：");
int b;
scanf("%d",&b);
int temp;
temp=del(head,b,sum);
if(temp==1){
    sum--;
}
output(head);

return 0; 

}

Answer 1

LNode* p = (LNode*)malloc(sizeof(LNode));//这样才是分配一块LNode大小的内存并定义指针指向该内存