Inserting a node at front and end of linked List

• Write a C program to insert a node at front of singly linked list.
• Write a C program to insert a node at the end of linked list.

Given a singly linked list having N nodes, we have to add a new node at front and back of a linked list. Here we will write two customer functions "insertAtFront" and "insertAtEnd" to add a new node at front and end of linked list respectively.

Singly linked list's node structure is as follows:

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

---

Inserting a node at the front of linked list

Algorithm to add a new node at front of linked list

• Dynamically create a new node using malloc function.
• Set data field of new node.
• Set the next pointer of new node to head of the linked list.
• Set new node as new head of linked list. Update head pointer.

/* 
Inserts a node in front of a singly linked list. 
*/
void insertAtFront(int num) {
    /* Create a new Linked List node */
    struct node* newNode = (struct node*) malloc(sizeof(struct node));
    newNode->data  = num;
    /* Next pointer of new node will point to head node of linked list  */
    newNode->next = head;
    /* make new node as new head of linked list */
    head = newNode;
    printf("Inserted Element : %d\n", num);
}

---

Inserting a node at the end of linked list

Algorithm to add a new node at front of linked list

• Dynamically create a new node using malloc function.
• Set data field of new node.
• Set next pointer of new node to NULL.
• Traverse from head node till tail node.
• Insert new after after tail node. Set next pointer of tail node to new node.

/*
Inserts a node after last node of linked list 
*/
void insertAtEnd(struct node* head, int num){
    /* Input validation */
    if (head == NULL) { 
       printf("Error : Invalid node pointer !!!\n");       
       return;  
    }
    /* creates a new node */
    struct node* newNode =(struct node*) malloc(sizeof(struct node));
    newNode->data  = num;
    newNode->next = NULL;
    /* Traverse from head to last node  */
    while(head->next != NULL)
       head = head->next;
    
    /* Insert newNode after Tail node */
    head->next = newNode;
}

---

C program to insert a node at the front and end of linked list

#include <stdio.h>
#include <stdlib.h>
 
/* A structure of linked list node */
struct node {
  int data;
  struct node *next;
} *head;

void initialize(){
    head = NULL;
}

/* 
Inserts a node in front of a singly linked list. 
*/
void insertAtFront(int num) {
    /* Create a new Linked List node */
    struct node* newNode = (struct node*) malloc(sizeof(struct node));
    newNode->data  = num;
    /* Next pointer of new node will point to head node of linked list  */
    newNode->next = head;
    /* make new node as new head of linked list */
    head = newNode;
    printf("Inserted Element : %d\n", num);
}

/*
Inserts a node after last node of linked list 
*/
void insertAtEnd(struct node* head, int num){
    /* Input validation */
    if (head == NULL) { 
       printf("Error : Invalid node pointer !!!\n");       
       return;  
    }
    /* creates a new node */
    struct node* newNode =(struct node*) malloc(sizeof(struct node));
    newNode->data  = num;
    newNode->next = NULL;
    /* Traverse from head to last node  */
    while(head->next != NULL)
       head = head->next;
    
    /* Insert newNode after Tail node */
    head->next = newNode;
}

/*
Prints a linked list from head node till tail node 
*/
void printLinkedList(struct node *nodePtr) {
    printf("\nLinked List\n");
  while (nodePtr != NULL) {
     printf("%d", nodePtr->data);
     nodePtr = nodePtr->next;
     if(nodePtr != NULL)
         printf("-->");
  }
}
 
int main() {
    initialize();
    /* Creating a linked List*/
    insertAtFront(2);  
    insertAtFront(4); 
    insertAtFront(5); 
    insertAtFront(9);
    printLinkedList(head);
    /* Inserting a node after tail node of Linked List */
    insertAtEnd(head, 10);
    printf("\n\nAfter Insertion At End\n");
    printLinkedList(head);
    return 0;
}

Output

Inserted Element : 2
Inserted Element : 4
Inserted Element : 5
Inserted Element : 9

Linked List
9-->5-->4-->2

After Insertion At End

Linked List
9-->5-->4-->8-->2-->10