大学生编码关于指针顺序表的疑惑

#include
#include
#include
typedef int DataType;
typedef struct {
    DataType* data;  // 指针方法，动态内存分配，即用类似用data【】来保存了元素(整体)，而不是用node来保存单个元素（链表）
    unsigned int length, capacity;
} SeqList;
int CreateSeqList(SeqList* sl)
{
    int i, elem;
    sl->length = 0;
    sl->capacity = 20;
    for (i = 0; i < sl->capacity; i++)
    {
        scanf_s("%d", &elem);
        if (elem != -1)
        {
            sl->data[i] = elem;
            sl->length++;
        }
        else
            break;
    }
    if (sl->length == 0) return 0;
    else return 1;
}
void InitSeqListP(SeqList* sl, unsigned int capacity = 50)
{
    sl->data = (int*)malloc(sizeof(sl->data));
    sl->length = 0;
    sl->capacity = capacity;
}
void PrintSeqList(SeqList* sl)
{
    for (int i = 0; i < sl->length; i++)
        printf("%d ", sl->data[i]);
    printf("\n");
}
int InsertSeqList(SeqList* sl, int i, DataType x)
{
    if (sl->length >= sl->capacity)
    {
        printf("上溢错误，插入失败\n");
        return 0;
    }
    else if (i > sl->length + 1 || i < 1)
    {
        printf("插入位置错误，插入失败\n");
        return 0;
    }
    else
    {
        for (int j = sl->length; j >= i; j--)
            sl->data[j] = sl->data[j - 1];
        sl->data[i - 1] = x;
        sl->length++;
        return 1;
    }
}
int DelSeqList(SeqList* sl, int i, DataType* rtn)
{
    if (sl->length == 0)
    {
        printf("下溢错误，删除失败\n");
        return 0;
    }
    else if (i > sl->length || i < 1)
    {
        printf("删除位置错误，删除失败\n");
        return 0;
    }
    else
    {
        *rtn = sl->data[i - 1];
        for (int j = i; j < sl->length; j++)
            sl->data[j - 1] = sl->data[j];
        sl->length--;
        return 1;
    }
}
int InsertSeqListSorted(SeqList* sl, DataType x)
{
    if (sl->length >= sl->capacity)
    {
        printf("上溢错误，插入失败\n");
        return 0;
    }
    else
    {
        int i = 0;
        for (; i < sl->length; i++)
        {
            if (x >= sl->data[i])
                continue;
            else if (x < sl->data[i])
                break;
        }
        i = i + 1;//插入的位置
        for (int j = sl->length; j >= i; j--)
            sl->data[j] = sl->data[j - 1];
        sl->data[i - 1] = x;
        sl->length++;
        return 1;
    }
}
int main()
{
    SeqList list;
    InitSeqListP(&list, 50);
    list.length = 0;
    int ptr;
    CreateSeqList(&list);
    PrintSeqList(&list);
    InsertSeqListSorted(&list, 6);
    PrintSeqList(&list);
    InsertSeqList(&list, 3, 99);
    PrintSeqList(&list);
    DelSeqList(&list, 5, &ptr);
    PrintSeqList(&list);
    printf("%d\n", ptr);
    return 0;
}

如图，指针法处理顺序表的测试时，输入之后结果也有，但为什么会弹出这个啊，大学生一枚。

改动处见注释，供参考：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef int DataType;
typedef struct {
    DataType* data;  // 指针方法，动态内存分配，即用类似用data【】来保存了元素(整体)，而不是用node来保存单个元素（链表）
    unsigned int length, capacity;
} SeqList;
int CreateSeqList(SeqList* sl)
{
    int i, elem;
                   //sl->length = 0;      修改
                   //sl->capacity = 20;   修改
    for (i = 0; i < sl->capacity; i++)
    {
        scanf("%d", &elem);
        if (elem != -1)
        {
            sl->data[i] = elem;
            sl->length++;
        }
        else
            break;
    }
    if (sl->length == 0) return 0;
    else return 1;
}
void InitSeqListP(SeqList* sl, unsigned int capacity = 50)
{
    sl->data = (DataType*)malloc(sizeof(DataType)*capacity); //修改
                        //sl->data = (int*)malloc(sizeof(sl->data));
    sl->length = 0;
    sl->capacity = capacity;
}
void PrintSeqList(SeqList* sl)
{
    for (int i = 0; i < sl->length; i++)
        printf("%d ", sl->data[i]);
    printf("\n");
}
int InsertSeqList(SeqList* sl, int i, DataType x)
{
    if (sl->length >= sl->capacity)
    {
        printf("上溢错误，插入失败\n");
        return 0;
    }
    else if (i > sl->length + 1 || i < 1)
    {
        printf("插入位置错误，插入失败\n");
        return 0;
    }
    else
    {
        for (int j = sl->length; j >= i; j--)
            sl->data[j] = sl->data[j - 1];
        sl->data[i - 1] = x;
        sl->length++;
        return 1;
    }
}
int DelSeqList(SeqList* sl, int i, DataType* rtn)
{
    if (sl->length == 0)
    {
        printf("下溢错误，删除失败\n");
        return 0;
    }
    else if (i > sl->length || i < 1)
    {
        printf("删除位置错误，删除失败\n");
        return 0;
    }
    else
    {
        *rtn = sl->data[i - 1];
        for (int j = i; j < sl->length; j++)
            sl->data[j - 1] = sl->data[j];
        sl->length--;
        return 1;
    }
}
int InsertSeqListSorted(SeqList* sl, DataType x)
{
    if (sl->length >= sl->capacity)
    {
        printf("上溢错误，插入失败\n");
        return 0;
    }
    else
    {
        int i = 0;
        for (; i < sl->length; i++)
        {
            if (x >= sl->data[i])
                continue;
            else if (x < sl->data[i])
                break;
        }
        i = i + 1; //插入的位置
        for (int j = sl->length; j >= i; j--)
            sl->data[j] = sl->data[j - 1];
        sl->data[i - 1] = x;
        sl->length++;
        return 1;
    }
}
int main()
{
    SeqList list;
    InitSeqListP(&list, 50);
                 //list.length = 0;  修改

    int ptr;
    CreateSeqList(&list);
    PrintSeqList(&list);

    InsertSeqListSorted(&list, 6);
    PrintSeqList(&list);

    InsertSeqList(&list, 3, 99);
    PrintSeqList(&list);

    DelSeqList(&list, 5, &ptr);
    PrintSeqList(&list);
    printf("%d\n", ptr);

    return 0;
}