C program to delete last node of Singly Linked List

Required knowledge

Algorithm to delete last node of Singly Linked List

Algorithm to delete last node of Singly Linked List
%%Input : head node of the linked list
Begin:
    If (head == NULL) then
        write ('List is already empty')
    End if
    Else then
        toDelete ← head
        secondLastNode ← head
        While (toDelete.next != NULL) do
            secondLastNode ← toDelete
            toDelete ← toDelete.next
        End while
        If (toDelete == head) then
            head ← NULL
        End if
        Else then
            secondLastNode.next ← NULL
        End else
        unalloc (toDelete)
    End else
End

Steps to delete last node of a Singly Linked List

1. Traverse to the last node of the linked list keeping track of the second last node in some temp variable say secondLastNode.
   
   
   
   
2. If the last node is the head node then make the head node as NULL else disconnect the second last node with the last node i.e. secondLastNode->next = NULL.
   
   
   
   
3. Free the memory occupied by the last node.
   
   
   
   

Program to delete last node of Singly Linked List

/**
 * C program to delete last node of Singly Linked List
 */

#include <stdio.h>
#include <stdlib.h>


/* Structure of a node */
struct node {
    int data; //Data part
    struct node *next; //Address part
}*head;



void createList(int n);
void deleteLastNode();
void displayList();



int main()
{
    int n, choice;

    /*
     * Creates a singly linked list of n nodes
     */
    printf("Enter the total number of nodes: ");
    scanf("%d", &n);
    createList(n);

    printf("\nData in the list \n");
    displayList();

    printf("\nPress 1 to delete last node: ");
    scanf("%d", &choice);

    /* Deletes the last node from list */
    if(choice == 1)
        deleteLastNode();

    printf("\nData in the list \n");
    displayList();

    return 0;
}



/*
 * Create a list of n nodes
 */
void createList(int n)
{
    struct node *newNode, *temp;
    int data, i;

    head = (struct node *)malloc(sizeof(struct node));

    /*
     * If unable to allocate memory for head node
     */
    if(head == NULL)
    {
        printf("Unable to allocate memory.");
    }
    else
    {
        /*
         * Reads data of node from the user
         */
        printf("Enter the data of node 1: ");
        scanf("%d", &data);

        head->data = data; //Links the data field with data
        head->next = NULL; //Links the address field to NULL

        temp = head;

        /*
         * Creates n nodes and adds to linked list
         */
        for(i=2; i<=n; i++)
        {
            newNode = (struct node *)malloc(sizeof(struct node));

            /* If memory is not allocated for newNode */
            if(newNode == NULL)
            {
                printf("Unable to allocate memory.");
                break;
            }
            else
            {
                printf("Enter the data of node %d: ", i);
                scanf("%d", &data);

                newNode->data = data; //Links the data field of newNode with data
                newNode->next = NULL; //Links the address field of newNode with NULL

                temp->next = newNode; //Links previous node i.e. temp to the newNode
                temp = temp->next;
            }
        }

        printf("SINGLY LINKED LIST CREATED SUCCESSFULLY\n");
    }
}



/*
 * Deletes the last node of the linked list
 */
void deleteLastNode()
{
    struct node *toDelete, *secondLastNode;

    if(head == NULL)
    {
        printf("List is already empty.");
    }
    else
    {
        toDelete = head;
        secondLastNode = head;

        /* Traverse to the last node of the list*/
        while(toDelete->next != NULL)
        {
            secondLastNode = toDelete;
            toDelete = toDelete->next;
        }

        if(toDelete == head)
        {
            head = NULL;
        }
        else
        {
            /* Disconnects the link of second last node with last node */
            secondLastNode->next = NULL;
        }

        /* Delete the last node */
        free(toDelete);

        printf("SUCCESSFULLY DELETED LAST NODE OF LIST\n");
    }
}



/*
 * Displays the entire list
 */
void displayList()
{
    struct node *temp;

    /*
     * If the list is empty i.e. head = NULL
     */
    if(head == NULL)
    {
        printf("List is empty.");
    }
    else
    {
        temp = head;
        while(temp != NULL)
        {
            printf("Data = %d\n", temp->data); //Prints the data of current node
            temp = temp->next; //Advances the position of current node
        }
    }
}