答案：

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
typedef int SLTDataType;
typedef struct SListNode {SLTDataType data;struct SListNode* next;
}SLTNode;
void PrintSLT(SLTNode* phead)    //打印单链表
{SLTNode* pcur = phead;while (pcur){printf("%d->", pcur->data);pcur = pcur->next;}printf("NULL\n");
}
SLTNode* SLTBuyNode(SLTDataType x)         //创建新结点
{SLTNode* newnode = (SLTNode*)malloc(sizeof(SLTNode));if (newnode == NULL)        //如果创建新结点失败{perror("malloc fail!");       //报错原因exit(1);              //结束退出}newnode->data = x;newnode->next = NULL;return newnode;
}
void SLTPushFront(SLTNode** pphead, SLTDataType x)     //头插
{assert(pphead);        //避免传进的二级指针为空SLTNode* newnode = SLTBuyNode(x);newnode->next = *pphead;           //头插*pphead = newnode;              //新结点为头结点
}
void SLTInsert(SLTNode** pphead, int i , SLTDataType x)       //在指定位置之前插入数据
{assert(pphead && *pphead);    //避免传入空的二级指针以及是空链表assert(i >= 0);SLTNode* newnode = SLTBuyNode(x);if (i == 0)        //如果是在头结点之前插入{SLTPushFront(pphead, x);    //调用头插函数}else {SLTNode* prev = *pphead;for (int n = 1; n <= i ; n++)     //遍历找到i之前的结点位置{	if (n == i)     //插入{newnode->next = prev->next;prev->next = newnode;}else         //继续遍历{prev = prev->next;}}}
}
void SLTErase(SLTNode** pphead, int i)   //删除第i个结点
{assert(pphead && *pphead);assert(i >= 0);if (i == 0)   //如果要删除头结点{SLTNode* next = (*pphead)->next;free(*pphead);*pphead = next;}else{SLTNode* p = *pphead;while (p->next != NULL && i--)    //利用短路特点，使得如果删除最后的NULL失败{if (i == 0){SLTNode* next = p->next;p->next = p->next->next;free(next);}else{p = p->next;}}if (i > 0){printf("该结点不存在\n");}}
}
void SLTFind1(SLTNode* phead,int i)         //查找第i个位置的值
{assert(phead);SLTNode* p = phead;while (i-- && p!=NULL){p = p->next;}if (p != NULL){printf("第i个的值为：%d\n", p->data);}else{printf("不存在第i个的值");}}
void SLTFind2(SLTNode* phead, SLTDataType y)     //查找y这个值的位置
{SLTNode* pcur = phead;int index = 0;while (pcur){if (pcur->data == y){printf("下标值为%d\n", index);return;}pcur = pcur->next;index++;}printf("没找到\n");
}
void SListDesTroy(SLTNode** pphead)    //销毁链表
{assert(pphead && *pphead);       //避免传入空的二级指针和空链表SLTNode* pcur = *pphead;while (pcur) {SLTNode* next = pcur->next;free(pcur);pcur = next;}*pphead = NULL;    //避免成为野指针
}
int main()
{//(1)SLTNode* plist = NULL;int n = 0;printf("请输入单链表的指定长度：\n");scanf("%d", &n);for (int i = 0; i < n; i++){int x = 0;scanf("%d", &x);SLTPushFront(&plist, x);}PrintSLT(plist);//(2)printf("请输入要插入的下标i和元素x：\n");int i = 0, x = 0;scanf("%d%d", &i, &x);SLTInsert(&plist, i, x);PrintSLT(plist);//(3)printf("请输入要删除的下标i:\n");scanf("%d", &i);SLTErase(&plist, i);PrintSLT(plist);//(4)printf("请输入要查找的位置i：\n");scanf("%d", &i);SLTFind1(plist, i);//(5)printf("请输入要查找的元素y：\n");int y = 0;scanf("%d", &y);SLTFind2(plist, y);//(6)销毁链表，归还申请空间SListDesTroy(&plist);printf("链表已销毁\n");return 0;
}