String wont store in linked list - c++

Question

#include <iostream>
#include <string.h>
using namespace std;
class MovieList {
private:
struct MovieNode {
string title;
struct MovieNode *next;
};
MovieNode *head;
public:
void appendNode(string var);
void displayList();
};
void MovieList::appendNode(string var) {
MovieNode *newNode, *nodePtr;
newNode = new MovieNode;
newNode->title = var;
newNode->next = NULL;
if (!head) {
head = newNode;
}
else {
nodePtr = head;
while (nodePtr->next)
nodePtr = nodePtr->next;
nodePtr->next = newNode;
}
cout << endl << "Input has been successfull!" << endl;
}
void MovieList::displayList() {
MovieNode *nodePtr;
if (head == NULL) {
cout << "The list is empty!" << endl;
}
else {
cout << "The nodes in the List are... " << endl;
nodePtr = head;
while (nodePtr) {
cout << nodePtr->title << endl;
nodePtr = nodePtr->next;
}
}
}
int main() {
MovieList list;
string var;
cout << " << Enter Movie >> " << endl << endl;
cout << "Enter a movie: ";
getline(cin, var);
list.appendNode(var);
list.displayList();
}
My question is why does the string variable won't show in the display void. The code is working at first when I try inputting a string but then it exits the program without displaying what I input. Is something wrong with how I put the string or is it in implementing the string into the node? please help, I'm new in linked list.

Answer 1

One issue is that MovieList.head is not initialized when you create a MovieList object.
Thus when MovieList.append() is called, this line:
if (!head)
causes the behavior of the program to be erratic due to the head pointer being whatever value it is, which you have no idea what the value is. It may be nullptr, thus the program works, but it may be any other values.
The bottom line is that you should initialize your member variables when you create an object. You can either create a default constructor that initialized head, or you can initialize head directly inline at the declaration point:
class MovieList
{
private:
struct MovieNode
{
string title;
struct MovieNode *next;
};
MovieNode *head;
public:
MovieList() : head(nullptr) {} // Using constructor
void appendNode(string var);
void displayList();
};
or:
class MovieList
{
private:
struct MovieNode
{
string title;
struct MovieNode *next;
};
MovieNode *head = nullptr; // Initialized here
public:
void appendNode(string var);
void displayList();
};