linked list insert and printing C++ - c++

Question

So i am trying to use double pointers to create insert function and then print the linked list.
I managed to do it with single pointers but this double pointer is driving me insane.
#include <iostream>
#include <string>
using namespace std;
class Node {
public:
string name;
int ID;
int marks[10];
Node *next;
};
void printOptions() {
cout << endl;
cout << "1.Insert New Node" << endl;
cout << "2.Print List" << endl;
cout << "3.Exit" << endl;
}
void insertAtBack(string inputName, Node **headref) {
Node **currentNodeRef;
currentNodeRef = headref;
while ((*currentNodeRef)->next != NULL) {
(*currentNodeRef) = (*currentNodeRef)->next;
}
(*currentNodeRef)->next = new Node();
(*currentNodeRef)->next->name = inputName;
(*currentNodeRef)->next->next = NULL;
}
void printList(Node *head) {
Node *indexNode;
indexNode = head;
while (indexNode != NULL) {
cout << (indexNode)->name << endl;
(indexNode) = (indexNode)->next;
}
}
int main() {
cout << "This implements a linked list" << endl;
int option;
bool infinite = true;
Node *head = NULL;
string testName;
while (infinite == true) {
printOptions();
std::cin >> option;
switch (option) {
case 1:
cout << "Enter student name" << endl;
std::cin >> testName;
if (head == NULL) {
head = new Node();
head->name = testName;
}
else {
insertAtBack(testName, &head);
}
break;
case 2:
printList(head);
break;
case 3:
exit(1);
break;
default:
exit(1);
break;
}
}
return 0;
}
So there is no compilation error or seg fault but instead the code runs it takes in 2 values and prints them fine. when the another value is typed inserted it only prints 2 values no more.
I think the print function is good because it worked previously with single pointer but i am not 100% sure.
I think the problem is in the insert function but i am not sire where.

Answer 1

void insertAtBack(string inputName, Node **headref) {
Node **currentNodeRef;
currentNodeRef = headref;
...
Node **currentNodeRef = headref; is an error. Remember you are passing the address of a pointer. You mean to write:
Node *currentNodeRef = *headref;
And change the function like so:
void insertAtBack(string inputName, Node **head)
{
Node *tail = *head;
while(tail->next != NULL)
tail = tail->next;
tail->next = new Node();
tail->next->name = inputName;
tail->next->next = NULL;
}
Also don't forget to initialize head->next = nullptr;
if (head == NULL) {
head = new Node();
head->name = testName;
head->next = nullptr; <--- add
}
It is better however if insertAtBack is prepared to handle head when head is NULL. The whole reason you pass Node **head is because you want a reference to the pointer so you can initialize it. So you can modify the code as:
void insertAtBack(string inputName, Node **head)
{
Node *new_node = new Node();
new_node->name = inputName;
new_node->next = nullptr;
if(*head)
{
Node *tail = *head;
while(tail->next)
tail = tail->next;
tail->next = new_node;
}
else
{
*head = new_node;
}
}
void printList(Node *head)
{
Node *node = head;
while(node)
{
cout << node->name << endl;
node = node->next;
}
}
int main()
{
cout << "This implements a linked list" << endl;
Node *head = NULL;
string testName;
while(true)
{
printOptions();
int option;
std::cin >> option;
switch(option)
{
case 1:
cout << "Enter student name" << endl;
std::cin >> testName;
insertAtBack(testName, &head);
break;
case 2: printList(head); break;
case 3: exit(1); break;
default: exit(1); break;
}
}
return 0;
}