[C]Why do we need double pointers for inserting in a link list

[Sporkman]

Instead do:

LLINK *t_last = NULL;

while(t!=NULL)
{
   t_last = t;
   t = t->next;
}

t_last->next = newnode;

[Sporkman]

...or:

while(t->next!=NULL)
{
   t = t->next;
}

t->next = newnode;

[dwhitney67]

Maintaining a pointer to the tail of the linked list would undoubtedly be more efficient than iterating node by node, until the end of the list is found.

Here's a basic example of using a tail pointer:

#include <stdlib.h>
#include <assert.h>

struct Node
{
   int          num;
   struct Node* next;
};

struct List
{
   struct Node* head;
   struct Node* tail;
};

void insert(struct List* list, int num)
{
   assert(list != 0);

   struct Node* elem = malloc(sizeof(struct Node));

   elem->num  = num;
   elem->next = 0;

   if (list->head == 0)
   {
      list->head = elem;
      list->tail = list->head;
   }
   else
   {
      list->tail->next = elem;
      list->tail = elem;
   }
}

int main()
{
   struct List list = {0, 0};

   insert(&list, 23);
   insert(&list, 11);
   insert(&list, 40);

   // ...

   return 0;
}