struct 
	{
	int total;
	char date[9];
	} customer_header;

struct 
	{
	int code;
	char name[41];
	char address[2][41];
	} customer_record;

#include <stdio.h>

/* Misc. data */

FILE *customer_file;

int open_customer()
	{ 
    /* Open as read/write */ 
	if ((customer_file = fopen("customer.dat", "r++")) == NULL)
		{
        /* Does not exist, try creating it */  
		if ((customer_file = fopen("customer.dat", "w++")) == NULL)
			{
			printf("Can't open customer.dat, error %d.\n", errno);
			exit(errno);
			}
        /* Write out a initial header record */
		memset(&customer_header, 0, sizeof (customer_header));
		write_customer_header();
		}
	else 
        /* Read the header record */
		fread(&customer_header, sizeof (customer_header), 1, customer_file);
	}


/* Write the header record */

int write_customer_header()
	{
	fseek(customer_file, 0L, 0);
	return fwrite(&customer_header, sizeof (customer_header), 1,
	    customer_file);
	}

/* Read record */

int read_customer(record)
int record;
	{
	fseek(customer_file, (long) record * sizeof (customer_record) 
		+ sizeof (customer_header), 0);
	return fread(&customer_record, sizeof (customer_record), 1,
	    customer_file);
	}

/* Write record */

int write_customer(record)
int record;
	{
	fseek(customer_file, (long) record * sizeof (customer_record) 
		+ sizeof (customer_header), 0);
	return fwrite(&customer_record, sizeof (customer_record), 1,
	    customer_file);
	}

/* Delete a record  (slow method ) */

int delete_customer(record)
int record;
	{
	int i;
	for (i = record;  i < customer_header.total - 1;  i++)
		{
		read_customer(i + 1);
		write_customer(i);
		}
	customer_header.total--;
	write_customer_header();
	}