如何在main中使用指针数组？

Question

I tried asking my question but I don't appear to be asking it correctly and I have been stuck for 2 months now. (which is sad)

For reference only: I built a linked list from nodes:

struct node  {
int number;
node *next;  }; 

To link these in main I used -> to assign values

void insertAsFirstElement(node *&head, node *&tail, int number){
node *temp = new node; 
temp->number = number;
temp->next = NULL; 
head = temp;
tail = temp; }

Now I am trying to make a skiplist, which should have the same structure as my original node except the node* next should be an array of pointers of type node.

struct node {
int number;
node *next[3];
};

I am getting confused on how to have an array of node pointers. I notice they tend to look like this: node **next and then declared to have memory allocated dynamically. I just want my arrays to be of size 4. So [3].

My problem is how can I create new nodes with the array of node pointers in main() and put something in the first slot of the nodes array?

This does not work for putting things in the array but it does work for putting in the number.

void insertAsFirstElement(node *&head, node *&tail, int number){

node *temp = new node; 
temp->number = number;
cout<<temp->number<<endl;
temp->next[0] = tail; 
cout<<temp->next[0]<<endl;
head->next[0] = temp;
cout<<head->next[0]<<endl;
}

Please help me.

Answer 1

The -> operator is a shorthand.

Without the -> operator, you would write

(*var).prop;

With the -> operator, you write:

var->prop;

Thus, to store a node in the first position of the list, you write:

void StoreNode(node *node){
    node *temp = new node;
    temp->next[0]=node;
}

And to retrieve data from a node in the list, you can write:

temp->next[0]->number

which is the same as writing

(*temp).next[0]->number

which is the same as writing

( *((*temp).next[0]) ).number

This line of your code seems a little confused:

void insertAsFirstElement(node *&head, node *&tail, int number){

Remember, you are just passing your function the address of a node. Therefore, all you need is

void insertAsFirstElement(node *head, node *tail, int number){

Inside the function itself, you will have to find the correct location in the list, that is when you get into the ** notations.

Answer 2

The code at a first look seems ok. An array of pointers is just that, an array of elements where each one is a pointer, and you use it exactly with the syntax your code shows.

Note however that when declaring an array of pointers inside a class the elements are not automatically initialized so you probably want to fix the elements that are not used yet to NULL. Moreover in a skip list you're probably going to need to know at which "level" the node has been inserted.

Are you sure your problem is in that part? Often with C++ a mistake doesn't appear right in the point it's done, but much later. This happens because of the "undefined behavior" rule of the language (aka "programmers never make mistakes").