Creating a linked list based on the number of elements requested by the user in C

Question

So I wanted to create a doubly linked circular list with the node structure:

typedef struct Node { //node structure
    int value;
    struct Node *next;
    struct Node *previous;
} node;

At first, I had created my list as follows:

//allocate memory for the nodes
    node *first = malloc(sizeof(*first));
    node *second = malloc(sizeof(*second));
    node *third = malloc(sizeof(*third));
    node *fourth = malloc(sizeof(*fourth));
    node *fifth = malloc(sizeof(*fifth));

    { //define the nodes and link them together.(circular linked list)
        first->value = 1;
        first->next = second;
        first->previous = fifth;

        second->value = 2;
        second->next = third;
        second->previous = first;

        third->value = 3;
        third->next = fourth;
        third->previous = second;

        fourth->value = 4;
        fourth->next = fifth;
        fourth->previous = third;

        fifth->value = 5;
        fifth->next = first;
        fifth->previous = fourth;
    }

But then I realized that I do not know if the list should consist of 5 elements and wanted to ask the user about the size of the list. The problem is that when I tried to implement a function called createList() and pass the list size as a parameter, I have no clue of how I should create a such list. I thought of creating a temporary pointer first with ->next and ->previous values as NULL but then how would I iterate through the input n and create new nodes if the next node is NULL?

Thanks

Answer 1

you have to create new node n(input size) times and append to the tail of the linked list, you can use any looping construct to create new nodes, below is a sample code. Edited: condition for circular doubly linked list, earlier i'vent notice that you have asked for circular dll, i thought it was simply dll.

#include<stdio.h>
#include<stdlib.h>
typedef struct Node { //node structure
    int value;
    struct Node *next;
    struct Node *previous;
} node;

void createList(struct Node ** head, int size) {

    // temp variable to iterate list
    struct Node *temp = *head;
    int val;
    while (size--) {
        scanf("%d", &val);


        if (temp == NULL) {
            // create head node for empty linked list;
            struct Node *node = (struct Node*)malloc(sizeof( Node));
            node->previous = NULL;
            node->next = NULL;
            node->value = val;
            *head = node;
            temp = node;
        } else {
            // if head node exists append the numbers at the end of the linkedlist
            struct Node *node = (struct Node*)malloc(sizeof(struct Node));
            node->previous = temp;
            node->next = NULL;
            node->value = val;
            temp->next = node;
            temp = temp->next;
        }
    }

    // for circular linked list
    temp->next = *head;
    (*head)->previous = temp;
}

void printList (struct Node *head) {
    node *temp = head;
    while (head->next != temp) {
        printf("%d\n", head->value);
        head = head->next;
    }
    // print last node
    printf("%d\n", head->value);
}
int main () {

    struct Node *head = NULL;
    int size;
    scanf("%d", &size);
    createList(&head, size);
    printList(head);
    return 0;
}