'（'令牌错误

Question

这项工作，但是我必须使用指针算法。

struct lsn
{
    char lsn_nm[50];
};

struct Student
{
    char name[20];
    char surname[20];
    char st_id[11];
    struct lsn* ls;
};

int main()
{
    int stdnt, drs;
    int i,j;
    printf("Number of students: ");
    scanf("%d", &stdnt);

    struct Student* arr = malloc(stdnt*sizeof(struct Student));
    for (i = 0; i < stdnt; i++)
    {
        printf("Number of lessons: ");
        scanf("%d", &drs);
        (arr+i)->ls = malloc(drs*sizeof(struct lsn));

        for (j=0;j<drs;j++)
        {
            printf("Name of Lesson: ");
            scanf("%s", (arr+i)->ls[j].lsn_nm);
        }
    }

    return 0;
}

如果我尝试这样：（arr + i）->（ls + j）.lsn_nm，则会收到错误消息“'（'令牌之前的预期标识符” 请帮助我。