linklist

#include <stdio.h>
#include <stdlib.h>
/*
https://www.learn-c.org/en/Linked_lists
https://www.tutorialspoint.com/data_structures_algorithms/linked_list_program_in_c.htm
https://www.log2base2.com/data-structures/linked-list/linked-list-in-c.html

*/

typedef struct node
{
  int value;
  struct node *next;
}node;

node *head = NULL;


void printlist( node *p)
{
  while (p != NULL)
  {
    printf("%d \n", p->value);
    p = p->next;
  }
}


void add(int i)
{
    if (!head)
    {
        head = malloc(sizeof( node));
        head->value = i;
        head->next = NULL;
    } else
    {
        node *n = malloc(sizeof( node));
        n->value = i;
        n->next = head;
        head = n;
    }
}

void push(int i)
{
    if (!head)
    {
        head = malloc(sizeof( node));
        head->value = i;
        head->next = NULL;
    } else
    {

    node * current = head;
    while (current->next != NULL)
    {
        current = current->next;
    }
    current->next = (node *) malloc(sizeof(node));
    current->next->value = i;
    current->next->next = NULL;
    }
}


int pop()
{
    int retval = -1;
    node * next_node = NULL;

    if (head == NULL)
    {
        return -1;
    }

    next_node = head->next;
    retval = head->value;
    free(head);
    head = NULL;
    head = next_node;

    return retval;
}

int rem()
{
    int retval = 0;

   if (head == NULL)
    {
        return -1;
    }

    if (head->next == NULL)
    {
        retval = head->value;
        free(head);
        head = NULL;
        return retval;
    }


    node * current = head;
    while (current->next->next != NULL)
    {
        current = current->next;
    }


    retval = current->next->value;
    free(current->next);
    current->next = NULL;
    return retval;

}


void deleteNone(int key)
{


    node* current = head;
    node* previous = NULL;


   if(head == NULL)
   {
      return ;
   }


   while(current->value != key)
   {
      if(current->next == NULL)
      {
         return ;
      } else
      {

         previous = current;
         current = current->next;
      }
   }


   if(current == head)
      head = head->next;
    else
      previous->next = current->next;


   free (current);
   current = NULL;
}

void deleteList()
{

    node* current = head;
    node* next;

   while (current != NULL)
   {
       next = current->next;
       free(current);
       current = next;
   }
   head = NULL;
}

int main()
{
   add(0);
   add(1);
   add(2);
   add(3);
   push(100);
   push(200);

   deleteNone(100);

   rem();


  printlist(head);
  deleteList();
  printlist(head);


}