Thread: Creating a Queue using Double Linklist

Hello.

I'm learning about creating a queue using double link list using a video tutorial. I wrote this code as seen in the video. I don't have the source file shown in the video. I checked the video to find whether I missed something, but couldn't find anything.

When I run the code, the first element is showing the address of head instead of the element.

What should I do to make the head.first point to the first created list? Further videos of this tutorial series make use of this code, so I am stuck here

Code:

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


typedef struct listItem {
    int data;
    struct listItem *next;
    struct listItem *prev;
}LISTITEM;


typedef struct listHDR {
    struct listItem *first;
    struct listItem *last;
}LISTHDR;


LISTHDR head;


void enqueue(LISTITEM *item) {
    LISTITEM *temp;


    temp = head.last;
    head.last - item;
    item->prev = temp;
    item->next = (LISTITEM*)&head;
    temp->next = item;
}


LISTITEM* dequeue() {
    LISTITEM *temp;


    temp = head.first;
    if(temp == (LISTITEM*)&head) {
        temp = NULL;
    }
    else {
        head.first = temp->next;
        head.last->prev = (LISTITEM*)&head;
    }
    return temp;
}


int main()
{
    LISTITEM *Temp;
    head.first = (LISTITEM*)&head;
    head.last = (LISTITEM*)&head;
    //head.data = -1;


    for(int i = 0; i < 3; i++) {


        Temp = (struct listItem*)malloc(sizeof(LISTITEM));
        Temp->data = i;
        enqueue(Temp);
    }


    printf("First element = %d\n", head.first->data);
    printf("Last element = %d\n", head.last->data);


    do {
        Temp = dequeue();


        if(Temp != NULL) {
            printf("Data: %d\n", Temp->data);
        }
        else {
            printf("EMPTY\n");
        }
    } while(Temp != NULL);


    return 0;
}