링크드 리스트 구현

#include<stdio.h>
#include<stdlib.h>
 
typedef struct Node {
    int data;
    Node* next;
}Node;
 
typedef struct List {
    int count;
    Node* front;
    Node* back;
}List;
 
List list;
 
void init(Node* node,int data,Node* next)
{
    node->data = data;
    node->next = next;
}
void push_front(int data)
{
    Node* now = (Node*)malloc(sizeof(Node));
    init(now, data, NULL);
 
    if (list.count == 0)
    {
        list.front = now;
        list.back = now;
    }
    else
    {
        now->next = list.front;
        list.front = now;
    }
 
    list.count++;
}
void push_back(int data)
{
    Node* now = (Node*)malloc(sizeof(Node));
    init(now, data, NULL);
 
    if (list.count == 0)
    {
        list.front = now;
        list.back = now;
    }
    else
    {
        list.back->next = now;
        list.back = now;
    }
 
    list.count++;
}
void pop_front()
{
    Node* now = (Node*)malloc(sizeof(Node));
    init(now, NULL, NULL);
 
    if (list.count == 0)
    {
        printf("list is empty\n");
        return;
    }
    else if (list.count == 1)
    {
        list.front = NULL;
        list.back = NULL;
        free(list.front);
    }
    else
    {
        now = list.front;
        list.front = list.front->next;
        free(now);
    }
 
    list.count--;
 
}
void pop_back()
{
    Node* now = (Node*)malloc(sizeof(Node));
    init(now, NULL, NULL);
 
    if (list.count == 0)
    {
        printf("list is empty\n");
        return;
    }
    else if (list.count == 1)
    {
        list.front = NULL;
        list.back = NULL;
        free(list.back);
    }
    else
    {
        for (now = list.front; now->next != list.back;)
        {
            now = now->next;
        }
 
        now->next = list.back->next;
        free(now->next);
        list.back = now;
    }
 
    list.count--;
}
 
void clear()
{
    Node* now = (Node*)malloc(sizeof(Node));
    init(now, NULL, NULL);
 
    while (list.count)
        pop_front();
}
void insert(int data,int goal)
{
    Node* now = (Node*)malloc(sizeof(Node));
    init(now, NULL, NULL);
    Node* new_node = (Node*)malloc(sizeof(Node));
    init(new_node, data, NULL);
 
    for (now = list.front; now != NULL;)
    {
        if (now->data == goal)
        {
            break;
        }
        now = now->next;
    }
 
    if (now == NULL)
    {
        printf("찾는 데이터가 없습니다\n");
        return;
    }
 
    new_node->next = now->next;
    now->next = new_node;
    list.count++;
}
void del(int data)
{
    Node* now = (Node*)malloc(sizeof(Node));
    init(now, NULL, NULL);
    Node* pre_node = NULL;
 
 
    for (now = list.front; now != NULL;)
    {
        if (now->data == data)
        {
            break;
        }
        pre_node = now;
        now = now->next;
    }
 
    if (now == NULL)
    {
        printf("찾는 데이터가 없습니다\n");
        return;
    }
 
    if (pre_node == NULL)
    {
        list.front = list.front->next;
        free(now);
    }
    else
    {
        pre_node->next = now->next;
        free(now);
    }
 
    list.count--;
    
}
 
void printList()
{
    Node* now = (Node*)malloc(sizeof(Node));
    init(now, NULL, NULL);
 
    printf("NULL -> ");
    for (now = list.front; now != NULL;)
    {
        printf("%d -> ", now->data);
        now = now->next;
    }
    printf("NULL\n");
}
 
int main(void)
{
    list.front = NULL;
    list.back = NULL;
    list.count = 0;
 
    int ch = -1;
 
    while (ch != 0)
    {
        printf("\n\n");
        printf("하고싶은 명령을 입력하세요:\n");
        printf("0번:종료 1번: push_front 2번:push_back 3번:pop_front 4번:pop_back 5번:insert 6번:delete 7번:clear 8번:print \n");
        scanf("%d", &ch);
        switch (ch)
        {
        case 1:
            int d;
            printf("삽입할 데이터를 입력하세요\n");
            scanf("%d", &d);
            push_front(d);
            break;
        case 2:
            printf("삽입할 데이터를 입력하세요\n");
            scanf("%d", &d);
            push_back(d);
            break;
        case 3:
            pop_front();
            break;
        case 4:
            pop_back();
            break;
        case 5:
            int k;
            printf("어떤 데이터를 가진 노드 뒤에 어떤 값을 추가할건가요?\n");
            scanf("%d %d", &d,&k);
            insert(k, d);
            break;
        case 6:
            printf("어떤 데이터를 가진 노드를 삭제할건가요?\n");
            scanf("%d", &d);
            del(d);
            break;
        case 7:
            clear();
            break;
        case 8:
            printList();
            break;
        default:
            break;
        }
    }
    
 
    return 0;
}