Linked List Printing 0 value at beginning c++ - c++

Question

I am refreshing my c++ by creating a simple linked list class. What I am having problems is when I try to print the list, there is a zero printing at the beginning of the list. How can I get rid of this? Also, I am having trouble with my second constructor. How would I go about this?`
Here is the code
List.h
#ifndef NODE_H
#define NODE_H
class List{
private:
typedef struct Node{
int data;
struct Node* next;
}* node;
node head;
int listLength;
public:
List();
List(int data, node nextLink);
void printList();
void push(int data);
void Delete(int d);
int listSize(void);
};
my List.cpp
#endif
#include "node.h"
#include <iostream>
using namespace std;
List::List(){
head->data=0;
head->next= NULL;
listLength=0;
}
List::List(int data, node nextLink){
head=NULL;
listLength++;
}
void List::push(int data){
if(head==NULL){
head->data=data;
head->next= NULL;
}
else{
node cursor = head;
while(cursor->next != NULL)
cursor = cursor -> next;
node newNode= new Node;
newNode->data=data;
newNode->next=NULL;
cursor->next= newNode;
}
listLength++;
}
void List::printList(){
node cursor=head;
while(cursor!=NULL){
//if(cursor->data==0){cursor=cursor->next;}
if(cursor->next==NULL){
cout<<cursor->data<<endl;
return;
}
else{
cout<<cursor->data<<" -> ";
cursor=cursor->next;
}
}
cout<<endl;
}
int main(){
List li;
li.push(2);
li.push(3);
li.push(0);
li.push(4);
li.printList();
return 0;
}

Answer 1

You never initialize your head node, so you're writing to unallocated memory in the code below.
if(head==NULL){
head->data=data;
head->next= NULL;
}
It should be:
if(head==NULL){
head = new Node; // added this line
head->data=data;
head->next= NULL;
}
You also probably want the first constructor
List::List(){
head->data=0;
head->next= NULL;
listLength=0;
}
to instead be
List::List(){
head = NULL;
listLength=0;
}
As for the second constructor, I assume you want something like this?
List::List(int data, node nextLink){
head = new Node;
head->data = data;
head->next = nextLink;
listLength = 1;
}
If not, could you better explain what you want?
I would also note that it would be generally considered good programming practice to create a constructor for the Node struct that initializes next to NULL, and then you wouldn't have to set it explicitly every time you create a new Node throughout your code.