doubly

#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 insert_at_fast()
{
    data *q = (data*)malloc(sizeof(data));
    printf("Enter your name: ");
    scanf(" %[^\n]s",q -> name);
    printf("Enter your roll: ");
    scanf("%d",&q -> roll);
    q -> pre = NULL;
    q -> next = NULL;
    list = head;
    list -> pre = q;
    q -> next = list;
    head = q;
    menu();
    return;
}
void insert_at_last()
{
    data *q = (data*)malloc(sizeof(data));
    printf("Enter your name: ");
    scanf(" %[^\n]s",q -> name);
    printf("Enter your roll: ");
    scanf("%d",&q -> roll);
    q -> pre = NULL;
    q -> next = NULL;
    list = head;
    while(list -> next != NULL)
    {
        list = list -> next;
    }
    list -> next = q;
    q -> pre = list;
    q -> next = NULL;
    menu();
    return;
}

 void insert_at_nth(int n)
{
    data *p = (data*)malloc(sizeof(data));
    printf("Enter your name: ");
    scanf(" %[^\n]s",p -> name);
    printf("Enter your name: ");
    scanf("%d",&p -> roll);
    p -> pre = NULL;
    p -> next = NULL;
    list = head;
    if(n == 1)
    {
        p -> next = list;
        list -> pre = p;
        head = p;
        menu();
        return;
    }
    else
    {
        int i;
        for(i=0; i<n-1; i++)
        {
            list = list -> next;
        }
        data *temp = list -> pre;
        temp -> next = p;
        p -> pre = temp;
        p -> next = list;
        list -> pre = p;
        menu();

    }
    return;
}
void delete_by_value(int n)
{
    list = head;
    while(list -> next != NULL)
    {
        if(head -> pre == NULL && list -> roll == n)
        {
            head = list -> next;
            head -> pre = NULL;
            free(list);
            menu();
            return;
        }
        else if(list -> roll == n)
        {
            data *temp = list -> pre;
            data *temp1 = list -> next;
            temp -> next = list -> next;
            temp1 -> pre = temp;
            free(list);
            menu();
            return;
        }
        list = list -> next;
    }
    data *temp1 = list -> pre;
    temp1 -> next = NULL;
    free(list);
    display();

    return;

}
void delete_by_pos(int n)
{
    int i;
    list = head;
    if(n==1)
    {
        head = list -> next;
        head -> pre = NULL;
        free(list);
        menu();
        return;
    }
    else
    {
        for(i=0; i<n-1; i++)
        {
            list = list -> next;
        }
        data *temp = list -> pre;
        temp -> next = list -> next;
        list->next->pre = temp->next;
        free(list);
        menu();
        return;
    }
}
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-1; i++)
        {
            list = list -> next;
        }
        printf("%s\n",list -> name);
        printf("%d\n",list -> roll);
        return;
    }
    menu();

}

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;
    }
    menu();
    return;


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

        int m;
        printf("\n1.Insert at first\n");
        printf("2.insert_at_last\n");
        printf("3.insert_at_nth\n");
        printf("4.delete_by_value\n");
        printf("5.search_by_value\n");
        printf("6.search_by_position\n");
        printf("7.display\n");
        printf("8.Exit\n");
        scanf("%d",&m);
        switch(m)
        {
        case 1:
        {
            insert_at_fast();
            break;
        }
        case 2:
        {
          insert_at_last();
           break;
        }
        case 3:
        {
            int x;
            scanf("%d" ,&x);

            insert_at_nth(x);

            break;
        }
        case 4:
        {
            int y;
            printf("Enter the value you want to delete : ");
            scanf("%d",&y);
            delete_by_value(y);
            break;
        }
        case 5:
            {
                int z;
                printf("Enter the value : ");
                scanf("%d",&z);
                search_by_value(z);
            }
        case 6:
            {
                int r;
                printf("Enter position : ");
                scanf("%d",&r);
                search_by_position(r);
            }
        case 7:
            {
                display();
            }
        case 8:
        {
            exit(0);
            break;
        }
        default:
        {
            printf("You Choose Wrong Option!!\a\nPlease choose a Correct Option\n");
            menu();
        }
        }


    }




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