C Exercises: Insert new node at the beginning in a doubly linked list

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

// Structure for a doubly linked list node
struct node {
    int num;
    struct node *preptr;
    struct node *nextptr;
} *stnode, *ennode;

// Function prototypes
void DlListcreation(int n);
void DlLinsertNodeAtBeginning(int num);
void displayDlList(int a);

int main() {
    int n, num1, a;
    stnode = NULL;
    ennode = NULL;
    printf("\n\n Doubly Linked List: Insert new node at the beginning in a doubly linked list:\n");
    printf("------------------------------------------------------------------------------------\n");

    printf(" Input the number of nodes : ");
    scanf("%d", &n);
    DlListcreation(n);  // Create a doubly linked list
    a = 1;
    displayDlList(a);  // Display the original doubly linked list

    printf(" Input data for the first node : ");
    scanf("%d", &num1);
    DlLinsertNodeAtBeginning(num1);  // Insert a new node at the beginning
    a = 2;
    displayDlList(a);  // Display the doubly linked list after insertion
    return 0;
}

// Function to create a doubly linked list
void DlListcreation(int n) {
    int i, num;
    struct node *fnNode;

    if (n >= 1) {
        stnode = (struct node *)malloc(sizeof(struct node));

        if (stnode != NULL) {
            printf(" Input data for node 1 : ");
            scanf("%d", &num);

            stnode->num = num;
            stnode->preptr = NULL;
            stnode->nextptr = NULL;
            ennode = stnode;

            // Create nodes and link them to form the doubly linked list
            for (i = 2; i <= n; i++) {
                fnNode = (struct node *)malloc(sizeof(struct node));
                if (fnNode != NULL) {
                    printf(" Input data for node %d : ", i);
                    scanf("%d", &num);
                    fnNode->num = num;
                    fnNode->preptr = ennode;
                    fnNode->nextptr = NULL;

                    ennode->nextptr = fnNode;
                    ennode = fnNode;
                } else {
                    printf(" Memory can not be allocated.");
                    break;
                }
            }
        } else {
            printf(" Memory can not be allocated.");
        }
    }
}

// Function to insert a new node at the beginning of the doubly linked list
void DlLinsertNodeAtBeginning(int num) {
    struct node *newnode;
    if (stnode == NULL) {
        printf(" No data found in the list!\n");
    } else {
        newnode = (struct node *)malloc(sizeof(struct node));
        newnode->num = num;
        newnode->nextptr = stnode;
        newnode->preptr = NULL;
        stnode->preptr = newnode;
        stnode = newnode;
    }
}

// Function to display the doubly linked list
void displayDlList(int m) {
    struct node *tmp;
    int n = 1;
    if (stnode == NULL) {
        printf(" No data found in the List yet.");
    } else {
        tmp = stnode;
        if (m == 1) {
            printf("\n Data entered in the list are :\n");
        } else {
            printf("\n After insertion, the new list is :\n");
        }
        while (tmp != NULL) {
            printf(" node %d : %d\n", n, tmp->num);
            n++;
            tmp = tmp->nextptr;
        }
    }
}