A List of Linked Lists

Hello guys ! Hope you're doing well.
I have faced a problem in declaring linked lists inside a linked list.
I made a picture because it speaks more than 1000 words :D

Here's my structure declaration:

Code:

---

typedef struct author *link;
struct author
{
      char name[20];
      link next;
      link down;
};
typedef link LIST;
typedef link pos_author;


typedef struct book *ptr;
struct book
{
      char tittle[20];
      int year;
      int page;
      ptr down;
};
typedef ptr pos_book;

---

But, the program won't compile because it generates an error in insert-function.
cannot convert `author*' to `book*' in assignment
cannot convert `book*' to `author*' in assignment

Here is the Inserting Function:

Code:

---

void insert(LIST L)
{
    char ch;
    do{
        printf("Author:  ");
       
        pos_author tmp=(pos_author)malloc(sizeof(struct author);
        scanf("%s",tmp->name);
        tmp->next=NULL;
       
        do{
        printf("Book: ");
        pos_book temp=(pos_book)malloc(sizeof(struct book));
        scanf("%s %d %d",temp->tittle,&temp->year,&temp->page);
        temp->down=NULL;
       
        temp->down=tmp->down; // EROOR
        tmp->down=temp;          //ERROR
       
        printf("\nAnother Book: [Y/N]  ");
        ch=getch();}while(ch=='Y'||ch=='y');
       
        tmp->next=L->next;
        L->next=tmp;
       
        printf("Another Author: [Y/N]  ");
        ch=getch();}while(ch=='Y'||ch=='y');
}

---

Looking forward to get an answer from you. Thanx in advance.

Code:

---

typedef struct author *link;
struct author
{
      char name[20];
      link next;
      link down;
};

---

Your "down" element has the wrong type. You want it to point to a "book" structure, so it should be of type "ptr" or "pos_book" or "struct book *".

Bye, Andreas

The first problem is you're creating a lot of pointer typedef's, which add very little, and obscure a lot.

The second problem is trying to do too much in one function.

Whenever I create linked list code, I start with a few simple utility functions to manage some of the detail.
Eg.

Code:

---

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

typedef struct book {
    char        title[20];
    int        year;
    int        pages;
    struct book *next;
} book;

typedef struct author {
    char            name[30];
    struct author  *next;
    struct book    *wrote;
} author;

// Functions to append a node to the end of a given list
// Add other functions to say
// - insert at start
// - insert in the middle
// - remove a node from a list
void appendAuthor ( author **list, author *node ) {
    author *temp = *list;
    if ( temp == NULL ) {
        *list = node;
    } else {
        while ( temp->next != NULL ) {
            temp = temp->next;
        }
        temp->next = node;
    }
}
void appendBook ( book **list, book *node ) {
    book *temp = *list;
    if ( temp == NULL ) {
        *list = node;
    } else {
        while ( temp->next != NULL ) {
            temp = temp->next;
        }
        temp->next = node;
    }
}

// Functions to allocate and initialise nodes
// of the appropriate types.
author *createAuthor ( void ) {
    author *a = malloc( sizeof(*a) );
    if ( a ) {
        strcpy(a->name,"Anon");
        a->next = NULL;
        a->wrote= NULL;
    }
    return a;
}

book *createBook ( void ) {
    book *a = malloc( sizeof(*a) );
    if ( a ) {
        strcpy(a->title,"Blank");
        a->pages = 0;
        a->year = 0;
        a->next = NULL;
    }
    return a;
}

void doit ( author **list ) {
    author *a = createAuthor();
    book  *b = createBook();
    appendAuthor(list,a);
    appendBook(&a->wrote,b);
}

int main(void)
{
    author  *list = NULL;
    doit(&list);
    return 0;
}

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