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  • 1 Post By AndiPersti
  • 3 Post By Salem

A List of Linked Lists

This is a discussion on A List of Linked Lists within the C Programming forums, part of the General Programming Boards category; Hello guys ! Hope you're doing well. I have faced a problem in declaring linked lists inside a linked list. ...

  1. #1
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    Aug 2012
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    1

    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

    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.
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    Last edited by kristjon_ciko; 08-15-2012 at 07:52 AM.

  2. #2
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    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
    kristjon_ciko likes this.

  3. #3
    and the hat of wrongness Salem's Avatar
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    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;
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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