#include<stdio.h>
#include<stdlib.h>
typedef struct std_info
{
    char name[50];
    int roll;
    struct std_info *pre;
    struct std_info *next;
} data;

data *head = NULL;
data *list = NULL;

void display()
{
    list = head;
    while(list != NULL)
    {
        printf("%s\n",list -> name);
        printf("%d\n",list -> roll);
        list = list -> next;
    }
}

void search_by_position(int m)
{
    int i;
    list = head;
    if(m==0)
    {
        printf("%s\n",list -> name);
        printf("%d\n",list -> roll);
        return;
    }

    else
    {
        for(i=0; i<m; i++)
        {
            list = list -> next;
        }
        printf("%s\n",list -> name);
        printf("%d\n",list -> roll);
        return;
    }

}

void search_by_value(int x)
{
    list = head;
    while(list != NULL)
    {
        if(list -> roll == x)
        {
            printf("%s\n",list -> name);
            printf("%d\n",list -> roll);
        }
        list = list -> next;
    }
    return;

}

void delete_by_pos(int n)
{
    int i;
    list = head;
    if(n==0)
    {
        head = list -> next;
        free(list);
        display();
        return;
    }
    else
    {
        for(i=0; i<n; i++)
        {
            list = list -> next;
        }
        data *temp = list -> pre;
        temp -> next = list -> next;
        free(list);
        display();
        return;
    }
}

void delete_by_valu(int n)
{
    list = head;
    while(list != NULL)
    {
        if(list -> roll == n)
        {
            data *temp = list -> pre;
            temp -> next = list -> next;
            free(list);
            display();
        }
        list = list -> next;
    }
    return;

}

void insert_nth(int n)
{
    int i;
    list = head;
    data *N = (data*)malloc(sizeof(data));
        scanf(" %[^\n]s",N -> name);
        scanf("%d",&N -> roll);
        N -> pre = NULL;
        N -> next = NULL;
    if(n==0)
    {
       N -> next = head;
       list = head;
        return;
    }
    else
    {
        for(i=0; i<n; i++)
        {
            list = list -> next;
        }
        data *temp = list -> next;
        N -> pre = temp;

        return;
    }
}

main()
{
    int n,i,m,x,y,z;
    printf("Enter your node amount: ");
    scanf("%d",&n);
    for(i=0; i<n; i++)
    {
        data *N = (data*)malloc(sizeof(data));
        scanf(" %[^\n]s",N -> name);
        scanf("%d",&N -> roll);
        N -> pre = NULL;
        N -> next = NULL;

        if(head == NULL)
        {
            head = N;
            list = head;
        }
        else
        {
            list -> next = N;
            N -> pre = list;
            list = N;
        }
    }

    display();

    printf("Enter your search position: ");
    scanf("%d",&m);
    if(m>n)
    {
        printf("Invalid position\n");
    }
    else
    {
        search_by_position(m);
    }
    printf("Enter your search value: ");
    scanf("%d",&x);
    if(x>n)
    {
        printf("Invalid position\n");
    }
    else
    {
        search_by_value(x);
    }
    printf("Enter your delete position: ");
    scanf("%d",&y);
    if(y>n)
    {
        printf("Invalid position\n");
    }
    else
    {
        delete_by_pos(y);
    }
     printf("Enter your delete value: ");
    scanf("%d",&z);
    if(z>n)
    {
        printf("Invalid value\n");
    }
    else
    {
        delete_by_valu(z);
    }

}