make the list a type itself

linked-list.c

@@ -94,6 +94,7 @@ int main(int argc, char *argv[]) {
   printf("list_length = %d\n", list_length(emptylist));
 
   list_t *foolist = malloc(sizeof(list_t));
+  list_init(foolist);
   list_node_t foo = { 1, NULL };
   list_add(foolist, &foo);