C - 链接列表程序给出错误“忽略返回值：‘scanf’”。如果发现其他错误还请指出

Question

我正在尝试编写代码来实现链表。程序将从用户处获取的值插入到链接列表中，直到用户退出执行。该值可以插入到头部、尾部或用户输入的任何自定义位置。

编译程序后，每次 scanf 都会出现错误“忽略返回值：'scanf'”。它还给出了一个错误，指出 scanf 不安全，请使用 scanf_s 代替。我通过在预处理器定义中添加“_CRT_SECURE_NO_WARNINGS”解决了这个问题。如果您发现其他错误，还请指出。

#include <stdio.h>
#include <stdlib.h>

typedef struct node {
    int data;
    struct node* next;
} node;

typedef enum position { First = 1, Custom, Last} position;
typedef enum process {Exit, Run} process;

node* insertFirst(node* ptrHead, int val)
{
    node* temp = NULL;
    node* newNode = (node*)malloc(sizeof(node));
    
    if (newNode == NULL)
    {
        exit(1);
    }
    else
    {
        if (ptrHead == NULL)
        {
            newNode->data = val;
            newNode->next = NULL;
            ptrHead = newNode;
        }
        else 
        {
            temp = ptrHead;
            newNode->data = val;
            newNode->next = temp;
            ptrHead = newNode;
        }
    }
    return ptrHead;
}

node* insertPos(node* ptrHead, int val, int loc)
{
    node* temp = ptrHead;
    node* newNode = (node*)malloc(sizeof(node));
    
    if (newNode == NULL)
    {
        exit(1);
    }
    
    for (int i = 0; i < loc; i++)
    {
        temp = temp->next;
    }
    newNode->data = val;
    newNode->next = temp->next;
    temp->next = newNode;

    return ptrHead;
}


node* insertLast(node* ptrHead, int val)
{
    node* temp = ptrHead;
    node* newNode = (node*)malloc(sizeof(node));

    if (newNode == NULL)
    {
        exit(1);
    }

    newNode->data = val;
    newNode->next = NULL;
    while (temp->next != NULL)
    {
        temp = temp->next;
    }
    temp->next = newNode;

    return ptrHead;
}

void printList(node* ptrHead)
{
    node* temp = ptrHead;

    while (temp->next != NULL)
    {
        printf("%d\n", temp->data);
        temp = temp->next;
    }
}

int countNodes(node* ptrHead)
{
    node* temp = ptrHead;
    int i = 0;
    while (temp->next != NULL)
    {
        temp = temp->next;
        i++;
    }
    return i;
}

int main()
{
    node* ptrHead = NULL;
    position location;
    int num = 0;
    int pos = 0;
    process state = Run;

    while (state == Run)
    {
        printf(" Welcome to my Linked List program. \n");
        if (ptrHead == NULL)
        {
            printf("Enter first element of the list \n");
            scanf("%d", &num);
            ptrHead = insertFirst(ptrHead, num);
        }
        else
        {
            printf(" Enter number to choose location: \n 1 -> First\n 2-> Custom\n 3-> Last\n");
            scanf("%d", &pos);
            if (pos == Custom)
            {
                printf("Please enter the number and the placement\n");
                scanf("%d", &num);
                scanf("%d", &location);
                if (location > countNodes(ptrHead))
                {
                    printf("Enter position less than %d\n", countNodes(ptrHead));
                }
                else
                {
                    ptrHead = insertPos(ptrHead, num, location);
                }

            }
            else if (pos == First)
            {
                printf("Please enter the number\n");
                scanf("%d", &num);
                ptrHead = insertFirst(ptrHead, num);
            }
            else if (pos == Last)
            {
                printf("Please enter the number\n");
                scanf("%d", &num);
                ptrHead = insertLast(ptrHead, num);
            }
            else
            {
                printf("Wrong position entry\n");
            }
        }
        printList(ptrHead);

        printf("Enter '1' to insert another value and '0' to quit execution\n");
        scanf("%d", &state);
    }
    return 0;
}