C program to delete first node of Singly Linked List

Write a C program to create a singly linked list of n nodes and delete the first node or beginning node of the linked list. How to delete first node from singly linked list in C language. Algorithm to delete first node from singly linked list in C. Steps to delete first node from singly linked list.

Required knowledge

Basic C programming, Functions, Singly Linked List, Dynamic memory allocation

Algorithm to delete first node from Singly Linked List

Algorithm to delete first node of Singly Linked List
%%Input:  head of the linked list
Begin:
    If (head != NULL) then
        toDelete ← head
        head ← head.next
        unalloc (toDelete)
    End if
End

Steps to delete first node from Singly Linked List

1. Copy the address of first node i.e. head node to some temp variable say toDelete.

   

2. Move the head to the second node of the linked list i.e. head = head->next.
   
3. Disconnect the connection of first node to second node.
   
4. Free the memory occupied by the first node.
   

Program to delete first node of Singly Linked List

/**
 * C program to delete first node from Singly Linked List
 */

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


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


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



int main()
{
    int n, choice;

    /*
     * Create 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 first node: ");
    scanf("%d", &choice);

    /* Delete first node from list */
    if(choice == 1)
        deleteFirstNode();

    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
    {
        /*
         * In data of node from the user
         */
        printf("Enter the data of node 1: ");
        scanf("%d", &data);

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

        temp = head;

        /*
         * Create 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; // Link the data field of newNode with data
                newNode->next = NULL; // Link the address field of newNode with NULL

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

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


/*
 * Deletes the first node of the linked list
 */
void deleteFirstNode()
{
    struct node *toDelete;

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

        printf("\nData deleted = %d\n", toDelete->data);

        /* Clears the memory occupied by first node*/
        free(toDelete);

        printf("SUCCESSFULLY DELETED FIRST NODE FROM 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); // Print data of current node
            temp = temp->next;                 // Move to next node
        }
    }
}

Enter the total number of nodes: 5
Enter the data of node 1: 10
Enter the data of node 2: 20
Enter the data of node 3: 30
Enter the data of node 4: 40
Enter the data of node 5: 50
SINGLY LINKED LIST CREATED SUCCESSFULLY

Data in the list
Data = 10
Data = 20
Data = 30
Data = 40
Data = 50

Press 1 to delete first node: 1

Data deleted = 10
SUCCESSFULLY DELETED FIRST NODE FROM LIST

Data in the list
Data = 20
Data = 30
Data = 40
Data = 50