Doubly Linked List

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

int flag=1;

typedef struct Node
{
    int data;
    struct Node *next;
    struct Node *prev;
} node;

void insert(node *pointer, int data)
{

    while(pointer->next!=NULL)
    {
        pointer = pointer -> next;
    }

    pointer->next = (node *)malloc(sizeof(node));
    (pointer->next)->prev = pointer;
    pointer = pointer->next;
    pointer->data = data;
    pointer->next = NULL;

    printf("\n    Data successfully inserted...");
}

void find(node *pointer, int data)
{
    pointer =  pointer -> next;

    while(pointer != NULL && flag != 0)
    {
        if(pointer->data == data)
        {
            flag = 0;
        }

        else
        {
            pointer = pointer -> next;
            flag = 1;
        }
    }
}

void update(node *pointer, int data)
{
    int new_data;
    printf("\n    Enter new data : ");
    scanf("%d", &new_data);

    pointer =  pointer -> next;

    while(pointer != NULL)
    {
        if(pointer->data == data)
        {
            pointer->data = new_data;
            printf("\n    Data update successful...");
        }

        pointer = pointer -> next;
    }

    return;
}

void delete(node *pointer, int data)
{

    while(pointer->next!=NULL && (pointer->next)->data != data)
    {
        pointer = pointer -> next;
    }

    if(pointer->next==NULL)
    {
        printf("\n    '%d' is not present in the list!\n", data);
        return;
    }

    node *temp;
    temp = pointer -> next;
    pointer->next = temp->next;
    temp->prev =  pointer;

    free(temp);

    printf("\n    Data successfully deleted...");

    return;
}
void print(node *pointer)
{
    if(pointer==NULL && flag == 1)
    {
        printf("\n    The list is empty!");
    }
    if(pointer == NULL)
    {
        return;
    }
    else
    {
        flag = 0;
        printf("%d ",pointer->data);
        print(pointer->next);
    }

    flag = 1;
}

int main(void)
{

    node *start,*temp;
    start = (node *)malloc(sizeof(node));
    temp = start;
    temp -> next = NULL;
    temp -> prev = NULL;

    printf("1. Insert\n2. Delete\n3. Print\n4. Find\n5. Update\n6. Terminate this program");

    while(flag!=0)
    {
        int query;
        printf("\n\nEnter your choice : ");
        scanf("%d", &query);

        if(query == 1)
        {
            int data;
            printf("\n    Enter your data : ");
            scanf("%d", &data);

            insert(start, data);
        }

        else if(query == 2)
        {
            int data;
            printf("\n    Enter the data that you want to delete : ");
            scanf("%d",&data);

            delete(start, data);
        }

        else if(query == 3)
        {
            printf("\n    List : ");
            print(start->next);
        }

        else if(query == 4)
        {
            int data;
            printf("\n    Enter the data that you want to find : ");
            scanf("%d",&data);

            find(start, data);

            if(flag == 0)
            {
                printf("\n    Found...");
            }
            else
            {
                printf("\n    Data is not in the list!");

            }
            flag = 1;
        }

        else if(query == 5)
        {
            int data;
            printf("\n    Enter the data you want to update : ");
            scanf("%d",&data);

            find(start, data);

            if(flag == 0)
            {
                printf("\n    Found...");
                update(start, data);
            }

            else
            {
                printf("\n    Data is not in the list!");
            }

            flag = 1;
        }

        else flag = 0;
    }

    printf("\n\nProgram terminated!\n\n");
}