// file: ll_set_0.cc//// isip include files//#include "link_list.h"#include "link_list_constants.h"// method: set_head_cc//// arguments://  Link_node* node : (input) a link node to set as head of list//// return: a logical_1 to indicate success//// this method sets the specified node at the head of the linked list//logical_1 Link_list::set_head_cc(Link_node* node_a) {  // exit ungracefully if the node is null  //  if (node_a == (Link_node*)NULL) {    return ISIP_FALSE;  }  // set this node at head  //  head_d = node_a;    // exit gracefully  //  return ISIP_TRUE;}