Sequential Dummynode

#include <stdio.h>
#include <stdlib.h>
#define TRUE 1
#define FALSE 0


typedef struct _node
{
    int data;
    struct _node* next;
} Node;

typedef struct _list
{
    Node* head;
    Node* curr;
    Node* back;
    int number;
    int (*comp)(int x, int y);
} List;

void Init(List* copy)
{
    copy->head = (Node*)malloc(sizeof(Node));
    copy->head->next = NULL;
    copy->comp = NULL;
    copy->number = 0;
}

void FInsert(List* copy, int data)
{
    Node* newNode = (Node*)malloc(sizeof(Node));
    newNode->data = data;

    newNode->next = copy->head->next;
    copy->head->next =newNode;

    (copy->number)++;
}

void SInsert(List* copy, int data)
{
    Node* newNode = (Node*)malloc(sizeof(Node));
    Node* pred = copy->head;
    newNode->data = data;

    while(pred -> next != NULL &&
        copy->comp(data, pred->next->data) != 0)
    {
        pred = pred->next;
    }

    newNode -> next = pred -> next;
    pred -> next = newNode;

    (copy->number)++;
}

void Insert(List* copy, int data)
{
    if (copy->comp == NULL)
        FInsert(copy, data);
    else
        SInsert(copy, data);
}

int First(List* copy, int* pdata)
{
    if(copy->head->next == NULL)
        return FALSE;
    
    copy->back = copy->head;
    copy->curr = copy->head->next;

    *pdata = copy->curr->data;
    return TRUE;
}

int Next(List* copy, int* pdata)
{
    if(copy->curr->next == NULL)
        return FALSE;
    
    copy->back = copy->curr;
    copy->curr = copy->curr->next;

    *pdata = copy->curr->data;
    return TRUE; 
}

int Remove(List* copy)
{
    Node* rpos = copy->curr;
    int rdata = rpos->data;

    copy->back->next = copy->curr->next;
    copy->curr = copy->back;

    free(rpos);
    (copy->number)--;
    return rdata;
}

int Count(List* copy)
{
    return copy->number;
}

void SetSortRule(List* copy, int (*comp)(int x, int y))
{
    copy->comp = comp;
}

int main(void)
{
    List list;
    int data;
    Init(&list);

    Insert(&list, 10);
    Insert(&list, 20);
    Insert(&list, 30);
    Insert(&list, 40);
    Insert(&list, 50);
    Insert(&list, 30);

    printf("Current Number of Data: %d\n", Count(&list));

    if(First(&list, &data)) // Search for First data
    {
        printf("%d ", data);

        while(Next(&list, &data))   // Search to after second data
            printf("%d ", data);
    }
    printf("\n\n");

    // Search and Remove Number 30
    if(First(&list, &data))
    {
        if(data == 30)
            Remove(&list);
        
        while(Next(&list, &data))
        {
            if(data == 30)
                Remove(&list);
        }
    }

    // After removed then Print entire data
    printf("Current Number of data: %d \n", Count(&list));

    if(First(&list, &data))
    {
        printf("%d ", data);

        while(Next(&list, &data))
            printf("%d ", data);
    }
    printf("\n\n");
    
    return 0;
}

/*
Current Number of Data: 6
30 50 40 30 20 10

Current Number of data: 4
50 40 20 10
*/