First<--null

AddFirst(newValue)
{
	Create the new Node newListItem
	newListItem.value <-- newValue
	newListItem.next  <--first
	first<--newListItem
}

AddLast(newValue)
{
Create the new Node newListItem
newListItem.value  newValue

If the list is empty Then
       first <-- newListItem
       newListItem.next <-- NULL
Else
	Create Nodes currentNode, previousNode
	while(currentNode!=NULL)
        {
           previousNode=currentNode;
            currentNode=currentNode->next;
       	}
        
        previousNode->next=newNode;
}

//Note that the operations from the in class assignment/homework are not included.
#include <stdio.h>
#include <stdlib.h>


/*keep track of the size of the list.
Initially, the size is 0,
thus  the count is 0.*/
int count = 0;

/*create a structure called "Node_n"
and give it a type definition
named Node.
We do this to avoid using the
"struct" keyword everytime
we declare a  Node_n structure.

It's simply a quality of life improvement
*/
typedef struct Node_n
{
    int data;
    struct Node_n * next;/*note that we cant
                        use the typedef here ,
                        e.g "struct Node * next;"
                        since the type definition
                        has not been created yet.
                        if used it will produce
                        a warning when you try to
                        assign Node Structures to
                        each other such as in the
                        add function etc:
                        "assignment from incompatible
                        pointer type
                         [-Wincompatible-pointer-types]|"
                             */
} Node;



/*we declare Node structure to
represent the first item at the
start of the list.

It is assigned a mull pointer value,
which can be thought of a value of
0 for the pointer.
*/
Node * first;

/*functionDeclarations 
that were IMPLEMWNTED 
in this code*/
void addFirst(int value);
void addLast(int value);
int size();
void printList();

/*functionDeclarations 
that were NOT IMPLEMENTED 
in this code. It was left 
for student discussion  
on how this should be implemented*/

void deleteNode(int location);//for delete(i) 
                              //algorithm from above                                
void insert(int value, int location);

int main()
{
    //initialization
    first=NULL;


    //codetesting
    addFirst(2);
    addFirst(1);
    addLast(3);
    addLast(4);
    printList();

    return 0;
}

void addFirst(int value)
{
    //create new node....
    /*we use malloc
        to allocate a portion  of
        RAM memory to store the
        data contained within a node.
        The amount of memory allocated is
        the size of the node datatype.


        the newly allocated node
        Node structure's pointer is now assigned
        to  our pointer named "newNode"

        note that "sizeof" is a unary operator
        much like the address operator "&"

        sizeof only requires parentheses
        only when  it is evaluating a data type
        so :

        int x;
        printf("%d", sizeof x);

        would complile and work fine.
        */


    Node * newNode = malloc(sizeof (Node));
    /*Question: how different would it be create
    new node without a pointer and achieve the
    same result in the line above?*/

    //.....store the data in the new node
    newNode->data=value;


    /*It is best practice to check to see of the list
    is empty and not based on the integer size being
    zero. This is because most list traversal happens
    through pointers  and must be stopped when null
    is reached. If using size to check if it's empty,
    the programmer may forget to set the last link
    in the list to be null resulting in infinite
    traversal looping*/
    //if the list is empty..
    if( first==NULL)
    {

        first=newNode;
        first->next=NULL;/*set next to null,
                        indicating that
                        this is the last item
                        in the list so far*/

    }
    else// the list contains items///
    {
        //create links..
        newNode->next=first;
        first=newNode;
        //recall that the list is null terminated still.
    }
    count++;
}

/*Future exercise 3:
adde a node called last which always
stores the last item in the list.
modify addFirst to ensure that
add first is being tracked.
modify this code to omit the
traversal using the while loop*/

void addLast(int value)
{
    /*What would happen if we used node
    structures instead of pointers?
    try to implement this function without
    delaring pointers,
    i.e declare newNode,currentNode,
    previousNode as a node and not a pointer
    to a Node
    Answer: when current is set to null, we will
    not be able to dereference the null value to
    a node so that current can now bw assigned
    to a NULL node. There is no such thing
    as a null struct, only null pointers*/
    Node * newNode = malloc(sizeof(Node));;

    newNode->data = value;
    newNode->next = NULL;

    //if the list is empty
    if(first==NULL)
        first=newNode;
    else
    {
        Node * currentNode , * previousNode;

        currentNode=first;
        previousNode=first;

        /*while  the end of the list
        has not been reached*/
        while(currentNode!=NULL)
        {
            previousNode=currentNode;
            currentNode=currentNode->next;
        }
        /*loop terminates with previousNode
        being the last one in the list
        */
        previousNode->next=newNode;
    }
    count++;
}

void printList()
{
    printf("Start list...\n");
    Node * current = first;
    while (current !=NULL)
    {
        printf("%d\n", current->data);
        current=(Node *)(current->next);
    }
    printf("End list...\n");
}



int size()
{
    return count;
}