Doubly Linked List - Understanding...

Hi, my first post.

I can´t understand the insert (or enqueue) operation in this algorithm where we work with Doubly Linked List with sort (ordering) during insert operation.

Could you help me please? I am putting comments in the lines where I have this difficulty to understand

Here is the code:

Code:

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typedef struct list
{
    int info;
    struct list *next;
    struct list *prev;
} list;

list *LHead, *LTail;

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Code:

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int value_info()
{
    int info;
 
    printf("\nValue = ");
    scanf("%d",&info);
    return info;   
}

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Code:

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void insert()
{
    list *p, *a, *q;
    int new;
   
    new = value_info();
   
    q = (list *)calloc(1,sizeof(list));
    q->info = new;
    p = LHead; //what does this mean???
    while (p->info < new) //what does this mean???
          p = p->next; //what does this mean???
    a = p->prev; //what does this mean???
    a->next = q; //what does this mean???
    p->prev = q; //what does this mean???
    q->next = p; //what does this mean???
    q->prev = a; //what does this mean???
    printf("Value %d inserted on list!",new);
}

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Cprogramming.com FAQ > Linked List Issues

Quote:

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Originally Posted by ಠ_ಠ

Cprogramming.com FAQ > Linked List Issues

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Look, thanks but

I see that this is a completely different way to add in order to the list, so I would need to change EVERYTHING in my code that works perfectly.

I just need to understand those last lines of insert opertation

Code:

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    while (p->info < new)
          p = p->next;
    a = p->prev;
    a->next = q;
    p->prev = q;
    q->next = p;
    q->prev = a;

---

I just need to generally interpret these lines. I would be very grateful if someone could explain just this insert operation

In your example, q is the new node. The while loop then iterates through the list until it finds a node with a higher int info in it. Then it inserts q by rearranging the pointers in the previous and next node, and setting it's own prev and next pointers appropriately.