Access violation in hotel booking assignment

I'm doing my assignment, a hotel booking system. In my cancel booking part, I'm getting an error:

Exception thrown at 0x00007FFA68272BE7 (ucrtbased.dll) in assignment 2.0.exe: 0xC0000005: Access violation reading location 0x0000000000000001.

I have removed the printf and file opening and closing at the point where I'm getting this error, but I can still see all the printfs . The part where it gets stuck is when i ask user to give a reason for cancellation.

I removed that part of code, and wrote printf("thankyou") but that doesn't appear. Yet the other printf I used before still appears on screen

void cancelBooking()
{
    FILE* bookf;  //file with booked room details
    FILE* tempf;
    char id[20];
    int cancel = 0;
    struct book b;
    int r;

    system("cls");

    //cleaning up/ flush
    while ((getchar()) != '\n');

    printf("\n----- BOOKING CANCELLATION  ------");
    printf("\n to cancel, enetr your user ID for verification: ");
    gets(id);
    //checking if user id matches
    if (strcmp(id, logged_in_user) == 0)
    {
        printf("\n user identified ");
        //to view booked room status
        view_status();
        printf("\n------------------------------------------------------------------------------------");

        //cleaning up/ flush
        while ((getchar()) != '\n');

        printf("\n enter your room no that you want to cancel: ");
        scanf("%d", &cancel);

        bookf = fopen("booked", "r");
        tempf = fopen("tempFile", "w");
        while (fread(&b, sizeof(b), 1, bookf))
        {
            r = b.roomNo;
            if (r != cancel)
            {
                fwrite(&b, sizeof(b), 1, tempf);
            }
        }

        fclose(bookf);
        fclose(tempf);

        //cleaning up/ flush
        while ((getchar()) != '\n');

        bookf = fopen("booked", "w");
        tempf = fopen("tempFile", "r");
        while (fread(&b, sizeof(b), 1, tempf))
        {
            fwrite(&b, sizeof(b), 1, bookf);
        }

        fclose(bookf);
        fclose(tempf);

        printf("\n BOOKING CANCELLED \n");

        //cleaning up/ flush
        while ((getchar()) != '\n');

        printf("\n thankyou");

        //going back to eithwr bookig menu or main menu
        going_back();
    }
    else
    {
        //cleaning up/ flush
        while ((getchar()) != '\n');

        while (strcmp(id, logged_in_user) != 0)
        {
            printf("\n -- non user cannot cancel booking -- ");
            printf("\n taking you back to BOOKING MENU");
            system("cls");
            display_booking_menu();
        }
    }

    //cleaning up/ flush
    while ((getchar()) != '\n');

}

I expect the code to move to "going back to main menus" but it is stuck at "thankyou" and wont move.