why am i not getting output - Data Structure , Linked List - c++

Question

I tried to get output after call insertNodeToEnd and displayNode. Bu I did not get any output. What is problem here?
#include <iostream>
using namespace std;
struct Node{
int data;
Node* next;
};
void displayNode(Node* head ){
while(head!=NULL){//starting pointimiz NULL olana kadar döndür
cout<<head->data<<endl; //NULL olana kadar her Node'un data'sını yazdı
head = head->next;//ilerle
}
}
void insertNodeToEnd(Node*curr , int data){
while(curr->next !=NULL){
curr = curr->next;
}
curr ->next ->data = data;
curr ->next->next = NULL;
}
Node* head; //başlangıc node'unun adresini tuttuk
int main(){
Node* Head = new Node; //bir node oluşturduk
Head -> next = NULL;
Head -> data = 500; //oluşan node'un datasını oluşturduk
Node *iter = Head; //linked list içerisinde dolşacak iterator
//bu iterator'u head olarak tuttuk(artık döngüde iter'i başlangıç olarak kullanacağız)
int i = 0;
for(i = 0 ; i<5 ; i++){
insertNodeToEnd(iter,i*10);
}
displayNode(Head);
}
I tried to get output after call insertNodeToEnd and displayNode. Bu I did not get any output. What is problem here?

Answer 1

The problem is your insertNodeToEnd() is implemented all wrong. It is not creating a new Node, it is accessing curr->next when it is not pointing at a valid node, and it is not taking into account the possibility of head being NULL when the list is empty.
Try something more like this instead:
#include <iostream>
using namespace std;
struct Node{
int data;
Node* next;
};
void displayNodes(Node* head){
while (head != NULL){
cout << head->data << endl;
head = head->next;
}
}
void insertNodeToEnd(Node* &head, int data){
Node *newNode = new Node;
newNode->data = data;
newNode->next = NULL;
if (head == NULL) {
head = newNode;
} else {
Node *curr = head;
while (curr->next != NULL) {
curr = curr->next;
}
curr->next = newNode;
}
}
/* alternatively:
void insertNodeToEnd(Node* &head, int data) {
Node **curr = &head;
while (*curr != NULL) {
curr = &((*curr)->next);
}
*curr = new Node;
(*curr)->data = data;
(*curr)->next = NULL;
}
*/
void freeNodes(Node* head){
while (head != NULL){
Node *next = head->next;
delete head;
head = next;
}
}
int main(){
Node* head = NULL;
insertNodeToEnd(head, 500);
for(int i = 0; i < 5; ++i){
insertNodeToEnd(head, i*10);
}
displayNodes(head);
freeNodes(head);
}
Online Demo
That being said, consider using the standard std::list container instead, eg:
#include <iostream>
#include <list>
using namespace std;
void displayNodes(const list<int> &lst){
for (int elem : lst){
cout << elem << endl;
}
}
int main(){
list<int> lst;
lst.push_back(500);
for(int i = 0; i < 5; ++i){
lst.push_back(i*10);
}
displayNodes(lst);
}
Online Demo