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

struct slistEl
{
    struct  slistEl * next;
    int data;
};


unsigned l_size(struct slistEl * p)
{
    int c = 0;

    while (p)
    {
        c++;
        p = p->next;
    }
    return c;
}


void l_printl(struct slistEl * p)
{
    int i;

    printf("Number of elements : %d", l_size(p));



    for (i = 1; p; p = p->next)
        printf("Element #%d  data %d\n", i++, p->data);
}


void l_push_front(struct slistEl **  head, int v)
{
    struct slistEl * p;

    p = (struct slistEl*) malloc(sizeof(struct slistEl));
    p->data = v;
    p->next = *head;
    *head = p;
}


void l_push_back(struct slistEl ** head, int v)
{
    struct slistEl *p, *e;

    e = (struct slistEl*) malloc(sizeof(struct slistEl));
    e->next = NULL;
    e->data = v;
    p = *head;
    if (p)
    {
        while (p->next) p = p->next;
        p->next = e;
    }
    else *head = e;
}


void l_insert_before(struct slistEl *  head, struct slistEl * e, int v)
{
    struct slistEl * p = head;

    if (p == e) l_push_front(&head, v);
    else
    {
        while (p->next != e) p = p->next;
        p->next = (struct slistEl*) malloc(sizeof(struct slistEl));
        p->next->next = e;
        p->next->data = v;
    }
}


void l_insert_after(struct slistEl * e, int v)
{
    struct slistEl * p = (struct slistEl*) malloc(sizeof(struct slistEl));

    p->next = e->next;
    p->data = v;
    e->next = p;
}


void l_pop_front(struct slistEl **  head)
{
    struct  slistEl * p = *head;

    if (p)
    {
        *head = p->next;
        free(p);
    }
}


void l_pop_back(struct slistEl *  head)
{
    struct  slistEl * p = head;

    if (p)
    {
        if (p->next)
        {
            while (p->next->next) p = p->next;
            free(p->next);
            p->next = NULL;
        }
        else
        {
            head = NULL;
            free(p);

        }
    }
}


void l_remove(struct slistEl * head, struct slistEl * e)
{
    struct slistEl * p;

    if (head == e) l_pop_front(&head);
    else
    {
        p = head;
        while (p->next != e) p = p->next;
        p->next = e->next;
        free(e);
    }
}

int main()
{

    struct slistEl * L = NULL;
    struct slistEl * e;
    int i;
    for (i = 1; i <= 7; i++) l_push_back(&L, i);
    l_printl(L);
    e = L;
    for (i = 1; i <= 3; i++) e = e->next;

    l_insert_before(L, e, 8);
    l_insert_after(e, 5);
    l_printl(L);
    l_remove(L, e);
    l_printl(L);
    l_pop_front(&L);
    l_printl(L);
    l_pop_back(L);
    l_printl(L);
}