Doubly Linked List

#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-1; 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==1)
    {
        head = list -> next;
        head -> pre = NULL;
        free(list);
        display();
        return;
    }
    else
    {
        for(i=0; i<n-1; 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 -> next != NULL)
    {
        if(head -> pre == NULL && list -> roll == n)
        {
            head = list -> next;
            head -> pre = NULL;
            free(list);
            display();
            return;
        }
        else if(list -> roll == n)
        {
            data *temp = list -> pre;
            data *temp1 = list -> next;
            temp -> next = list -> next;
            temp1 -> pre = temp;
            free(list);
            display();
            return;
        }
        list = list -> next;
    }
    data *temp1 = list -> pre;
    temp1 -> next = NULL;
    free(list);
    display();

    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;
        display();
        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;
        display();

    }
    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;
    display();
    return;
}

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;
    display();
    return;
}

main()
{
    int n,i,m,x,y,z,k,t;
    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;
        }
    }
    printf("............................\n");
    display();
    printf("............................\n");
    printf("Enter your search position: ");
    scanf("%d",&m);
    if(m>n)
    {
        printf("Invalid position\n");
    }
    else
    {
        search_by_position(m);
    }
    printf("...........................\n");
    printf("Enter your search value: ");
    scanf("%d",&x);
    if(x>n)
    {
        printf("Invalid position\n");
    }
    else
    {
        search_by_value(x);
    }
    printf("...........................\n");
    printf("Enter your delete position: ");
    scanf("%d",&y);
    if(y>n)
    {
        printf("Invalid position\n");
    }
    else
    {
        delete_by_pos(y);
    }
    printf("...........................\n");
    printf("Enter your delete value: ");
    scanf("%d",&z);
    if(z>n)
    {
        printf("Invalid value\n");
    }
    else
    {
        delete_by_valu(z);
    }
    printf("...........................\n");
    printf("Enter your value for add node: ");
    scanf("%d",&t);
    insert_at_nth(t);
    insert_at_last();
    insert_at_fast();
    return 0;
}