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

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

struct node* insertatfirst(int data,struct node* head){
    struct node* ptr= (struct node*)malloc(sizeof(struct node));
    ptr->next=head;
    ptr->data=data;
}

struct node* insertafternode(int data,struct node* prevnode,struct node* head){
    struct node* ptr= (struct node*)malloc(sizeof(struct node));
    ptr->data=data;
    ptr->next=prevnode->next;
    prevnode->next=ptr;
    

}

struct node* insertatindex(int data,struct node* head,int index){
    struct node* ptr= (struct node*)malloc(sizeof(struct node));
    struct node* p=head;
    int i=0;
    while(i!= index-1){
        p=p->next;
        i++;
    }
    ptr->data=data;
    ptr->next=p->next;
    p->next=ptr;

}

struct node* insertatend(int data,struct node* head){
    struct node* ptr= (struct node*)malloc(sizeof(struct node));
    struct node* p=head;
    while(p->next!=NULL){
        p=p->next;
    }
    ptr->data=data;
    p->next=ptr;
    ptr->next=NULL;
}

void linkedlisttraversal(struct node* ptr){
    while(ptr!=NULL){
    printf("%d  ",ptr->data);
    ptr=ptr->next;}
}
int main(){
    struct node* head;
    struct node* second;
    struct node* third;
    head=(struct node*)malloc(sizeof(struct node));
    second=(struct node*)malloc(sizeof(struct node));
    third=(struct node*)malloc(sizeof(struct node));
    head->data=7;
    head->next=second;
    second->data=17;
    second->next=third;
    third->data=77;
    third->next=NULL;
    printf("initial value \n");
    linkedlisttraversal(head);
    //head=insertatfirst(48,head);
    insertatindex(25,head,2);
    insertatend(89,head);
    head=insertafternode(26,second,head);
    printf(" \nfinal value \n");
    linkedlisttraversal(head);  
}