delete

void delete_first(NodeT** head, NodeT** tail)
{
    //TODO: delete first list element
    if(*head==NULL)
        return;
    else{
        NodeT *p=*head;
        *head=(*head)->next;
        free(p);
    }
}

void delete_last(NodeT** head, NodeT** tail)
{
    //TODO: delete last list element
    NodeT*p=*head;
    NodeT*prev=NULL;

    if(*head==NULL)
        return;

    while(p!=*tail)
    {
        prev=p;
        p=p->next;
    }
    if(p==*head)
    {
        *head=NULL;
        *tail=NULL;
    }
    prev->next=NULL;
    *tail=prev;

}