Doubly Linked List with C. Applications: Operating System management, Browser page path, File Explorer path

doubly_linkedlist.c

/*
 * Doubly Linked list
 * @copyright: Rafiul Islam
 *
*/

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

/*
 * A structure with 2 pointer that link next and previous node
 * and a integer value container.
 *
 * #Note#: Linked list insert by front. There next means initial
 *         last node that inserted before current and previous means
 *         initial next node that inserted after current one.
*/
struct List
{
    int value;
    struct List *next;
    struct List *prev;
};

/*
 * Create a head pointer for pointing current node and
 * initialized it with NULL (@see main function)
*/
struct List *head;

/*
 * Function prototype
*/
void add(int item);
void pop_back();
void showCurrent();

void main()
{
    head = NULL; //head pointer initialization

    /*
     * This block should print:
     * Current: 20
     * Next: 10
     * Previous: No element
    */
    add(10);
    add(20);
    showCurrent();

    /*
     * This block should print:
     * Current: 10
     * Next: No element
     * Previous: No element
    */
    pop_back();
    showCurrent();

    /*
     * @see Head link change
     * This block should print:
     * Current: 30
     * Next: 40
     * Previous: 20
    */
    add(20);
    add(30);
    add(40);
    head = head->next;
    showCurrent();
}

void add(int item)
{
    /*
     * Create a new member node, set the item value.
     * member->next should be current head
     * member->previous should be null always
     * when current head has any node then this current node
     * should link its previous to member by this way
     * head->previous(current->previous) = member
     * Finally head will point new member by head=member
    */
    struct List *member = (struct List*)malloc(sizeof(struct List));
    member->value = item;
    member->next = head;
    member->prev = NULL;
    if(head != NULL)
        head->prev = member;
    head = member;
}
void pop_back()
{
    /*
     * When list is not empty then point the head with a new
     * pointer and move head pointer to its next one. Then release
     * the last element with the new pointer.And set current
     * head->previous = NULL as there are no more element on this way.
    */
    if(head == NULL)
    {
        puts("No element available");
        return;
    }
    struct List *member = (struct List*)malloc(sizeof(struct List));
    member = head;
    head = member->next;
    free(member);
    if(head == NULL)
        return;
    head->prev = NULL;
}
void showCurrent()
{
    if(head == NULL)
    {
        puts("List empty\n-------------------------------");
    }
    else
    {
        printf("Current value: %d\n",head->value);
        head->prev == NULL ?
            puts("No previous"):
            printf("Previous value: %d\n",head->prev->value);

        head->next == NULL ?
            puts("No next"):
            printf("Next value: %d\n",head->next->value);
        puts("----------------------------------------");
    }
}