Linked list operations using double pointers

linked_list_double_pointer.cpp

#include<iostream>
using namespace std;

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

bool compare(node* new_node, node* existing_node)
{
  if (existing_node->data > new_node->data)
    return false;
  return true;
}

bool compare_delete(int data, node* existing_node)
{
  if(existing_node->data == data)
    return false;
  return true;
}

void DeleteSortedNode(int data)
{
  node **pp_node = &root_node; // Double pointer pp_node is always
                               // pointing to the pointer to a node.
                               // In the beginning it is pointing
                               // to head which is pointing to the
                               // first node. In the subsequent iterations
                               // it is pointing to the 'next' pointer
                               // of a node which is pointing to the
                               // next node, which allows checking the
                               // next node from the current node.
  
  while(*pp_node != NULL && compare_delete(data, *pp_node))
  {
    pp_node = &(*pp_node)->next;
  }
  node *temp = *pp_node;
  *pp_node = (*pp_node)->next;
  delete(temp);
}

void AddSortedNode(node* new_node, bool debug=false)
{
  node** pp_node = &root_node;
  while(*pp_node != NULL && compare(new_node,*pp_node))
  {
    pp_node = &(*pp_node)->next;
  }
  new_node->next = *pp_node;
  *pp_node = new_node;
}

void print_list()
{
  node* temp_node = root_node;
  while(temp_node != NULL)
  {
    cout<<temp_node->data<<" ";
    temp_node = temp_node->next;
  }
  cout<<endl;
}

int main()
{
  node* temp = new node();
  temp->data = 1;
  temp->next = NULL;
  AddSortedNode(temp);
  temp = new node();
  temp->data = 2;
  temp->next = NULL;
  AddSortedNode(temp);
  temp = new node();
  temp->data = 3;
  temp->next = NULL;
  AddSortedNode(temp);
  temp = new node();
  temp->data = 4;
  temp->next = NULL;
  AddSortedNode(temp);
  temp = new node();
  temp->data = 6;
  temp->next = NULL;
  AddSortedNode(temp);
  temp = new node();
  temp->data = 7;
  temp->next = NULL;
  AddSortedNode(temp);
  print_list();
  temp = new node();
  temp->data = 5;
  temp->next = NULL;
  AddSortedNode(temp, true);
  print_list();
  DeleteSortedNode(4);
  print_list();
  return 0;
}