Pointers C Linkedlist Adding Always NULL -

i've written function adding end of singly linked list in c. don't why if head element null, why continues remaining null after successive adds.

the struct defined this:

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

in main have this:

node test = null; add(test,1); add(test,2); add(test,3); 

function add defined such:

void add(node head, int newdata) {     node n = createnode(newdata);     if (head==null) {         head = n;         return;     }     else {         node tmp = head;         while (tmp->next != null) {            tmp = tmp->next;         }         tmp = n;     } } 

createnode defined thus:

node createnode(int data) {     node n = (node) malloc(sizeof(struct node));     n->next = null;     n->data = data;     return n; } 

what confused that, add function works fine if first initialize head (node test = createnode(1)) , proceeds add rest of values alright. if leave test node null, doesn't add values? happening here?

write function add following way

void add( node *head, int newdata )  {     node n = createnode( newdata );      while ( *head ) head = &( *head )->next;      *head = n; } 

or can write following way

void add( node *head, int newdata )  {     while ( *head ) head = &( *head )->next;      *head = createnode( newdata ); } 

and call like

node test = null;  add( &test, 1 ); add( &test, 2 ); add( &test, 3 ); 

take account function createnode must declared before function add , missed semicolon in structure definition

struct node {     int data;     node next; } ^^^ 

also not idea use same identifier struture tag , pointer same structure

typedef struct node* node; 

at least better write like

typedef struct node* node_ptr;