数组越界导致的数据异常

#include <stdio.h>
#include <windows.h>
#define Listsize 10

struct Seqlist
{
    int data[Listsize]; /* 向量data用于存放表结点 */
    int length;         /*  当前的表长度 */
};

void Initlist(struct Seqlist *L)
{
    memset(L, 0, sizeof(int) * Listsize);
    L->length = 0;
}

/* 将新结点x插入L所指的顺序表的第i个结点ai的位置上 */
void Insert(struct Seqlist *L, int data, int index)
{
    if (index < 0 || index > Listsize)
    {
        printf("error\n");
        return;
    } //输入非法
    for (int i = L->length; i >= index; i--)
        L->data[i + 1] = L->data[i];
    L->data[index] = data;
    L->length++;
}

void Print(struct Seqlist *L)
{
    for (int i = 0; i < Listsize; i++)
        printf("%d ", L->data[i]);
    printf("L->length:%d ", L->length);
    printf("\n");
}

void main()
{
    struct Seqlist *L;
    L = (struct Seqlist *)malloc(sizeof(struct Seqlist));
    Initlist(L);
    for (int i = 0; i < Listsize; i++)
    {
        Insert(L, i, i);
        Print(L);
    }
}

for (int i = L->length; i > index; i--)
        L->data[i + 1] = L->data[i];
    L->data[index] = date;
    L->length++;