Circular Singly Linked List with C. Application:: Round Robin Scheduler in OS for time sharing method and many more real life application

circular_singly_linkedlist.c

/*
 * Circular Singly Linked list
 * @copyright: Rafiul Islam
 *
*/

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

struct List
{
    int value;
    struct List *next;
};

/*
 * This program need two List pointer, one for point the head of the list.
 * Another for link the tail value. Tail pointer will always link head as
 * its next location for circular traverse.
*/
struct List *head, *tail;

void add(int item);
void pop();
void showTop();

void main()
{
    head = tail = NULL; //initially both are NULL
    showTop();

    add(45);
    showTop();

    add(78);
    add(97);
    showTop();

    pop();
    showTop();

    pop();
    showTop();
}
void add(int item)
{
    struct List *member = (struct List*)malloc(sizeof(struct List));
    member->value = item;
    /*
     * For first time of insertion in list make the member tail of the list.
     * First member always link itself as its next member for circulation
     * maintain. Otherwise new member will link its next to head and tail will
     * link this new member as tail next. Finally head will link this new member.
    */
    if(head == NULL)
    {
        tail = member;
        member->next = member;
    }
    else
    {
        member->next = head;
        tail->next = member;
    }
    head = member;
}
void pop()
{
    /*
     * Access the last member of the list, change the head link to previous one,
     * link tail next to updated head and then free the current member.
    */
    struct List *member = (struct List*)malloc(sizeof(struct List));
    member = head;
    head = member->next;
    tail->next = head;
    free(member);
}
void showTop()
{
    if(head == NULL)
    {
        puts("No Element !\n-------------------------------");
    }
    else
    {
        printf("Head value: %d\n",head->value);
        printf("Tail value: %d\n",tail->value);
        printf("Tail Linked value: %d\n",tail->next->value);
        puts("-------------------------------------------");
    }
}