// file: ll_insert_0.cc//// isip include files//#include "link_list.h"#include "link_list_constants.h"// method: insert_cc//// arguments://  Link_node* node : (input) a link node to insert in the list//// return: a logical_1 to indicate success//// this method inserts the specified node at the end of the linked list//logical_1 Link_list::insert_cc(Link_node* node_a) {  // exit ungracefully if the node is null  //  if (node_a == (Link_node*)NULL) {    return ISIP_FALSE;  }  // if there is no node present set this at head  //  if (head_d == (Link_node*)NULL) {    head_d = node_a;  }    // otherwise insert the new node at the end of the list  //  else {    curr_d->insert_cc(node_a);  }    // set the current position to the end  //  curr_d = node_a;  // exit gracefully  //  return ISIP_TRUE;}