Linked List Only Showing Last Value Entered - c++

Question

I am trying to become a little more adept with linked lists. I've watched several videos and read multiple forum posts, but I am still having issues. I am trying to start with a simple linked list. However, with my current code only the last value prints. I would really appreciate if someone could explain to me what I have done wrong. Also, I usually define all my functions in the main.cpp file. However, it would not let me do this for my linked list. Also, is defining all functions in the main.cpp file a good practice or a habit I should break?
Thanks in advance :).
Below is my linkedlist file:
#pragma once
#include <iostream>
using namespace std;
class LinkedList {
struct node {
int data;
node *next;
};
public:
LinkedList() {
head = NULL;
}
node *newNode;
node *temp;
node *head;
void insertData(int value) {
newNode = new node;
newNode->data = value;
temp = newNode;
head = newNode;
temp->next = newNode;
temp = temp->next;
newNode->next = NULL;
}
void printList() {
node *print;
print = head;
while (print != NULL) {
cout << print->data;
print = print->next;
}
}
};
Here is my main.cpp file
#include <iostream>
#include "LinkedList.h"
using namespace std;
int main() {
LinkedList list;
list.insertData(1);
list.insertData(2);
list.insertData(3);
list.printList();
system("pause");
return 0;
}

Answer 1

void insertData(int value) {
newNode = new node;
newNode->data = value;
temp = newNode;
head = newNode;
temp->next = newNode;
temp = temp->next;
newNode->next = NULL;
}
In your code, head = newNode takes whatever head was pointing to, and throws it out in favor of newNode. Essentially, every time you try to insert a new value into the list, you discard the whole list.
Rather, your insert should do something like
void insertData(int value) {
newNode = new node; //Create ourselves a new node
newNode->data = value; //Put the proper value in
newNode->next = head; //Make it so the whole list is after our node
head = newNode; //Make our node the first in the list
}
There are some other things in your code I would advise changing, like the fact that you have newNode and temp as member variables when they could simply be local to the functions, and your lack of a destructor. But your print function should work with the modified insert (see it run here).