Inserting a node after a given node in linked List

• Write a C program to add a node after a given node in linked list.

Given a singly linked list having N nodes, we have to add a new node after a given node of a linked list. Here we will write one customer functions "insertAfter" which adds a node after passed node of linked list..

Singly linked list's node structure is as follows:

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

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Algorithm to add a new node after a given node
We want to insert a new node after "previousNode";

• Dynamically create a new node using malloc function.
• Set data field of new node.
• Set the next pointer of new node to the next pointer of previousNode.
• Set next pointer of previousNode to new node.

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C program to insert a node after a given node in 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;
}

/* 
Given a Inserts a node in front of a singly linked list. 
*/
void insert(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);
}


void insertAfter(struct node* prevNode, int num) { 
    /* Input validation */
    if (prevNode == NULL) { 
       printf("Error : Invalid node pointer !!!\n");       
       return;  
    }  
         
    /* creates a new node */
    struct node* newNode =(struct node*) malloc(sizeof(struct node));
    newNode->data  = num;
    /* Set Next pointer of newNode to next pointer of nodePtr */
    newNode->next = prevNode->next;  
    /* Set next pointer of prevNode to newNode */
    prevNode->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*/
    insert(2);  
    insert(4); 
    insert(5); 
    insert(9);
    printLinkedList(head);
    /* Inserting a node after third node(4) from head */
    insertAfter(head->next->next, 8);
    printf("\n\nAfter Insertion\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

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