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

#define DATA_PORT 0x378 /* parallel port base address */
#define STATUS_PORT DATA_PORT + 1
#define CONTROL_PORT DATA_PORT + 2

unsigned char status, data;

void main()
{
    if (ioperm(DATA_PORT, 1, 1))
    {
        fprintf(stderr, "Access denied to %x\n", DATA_PORT), exit(1);
    }

    while (1)
    {
        for (int seg = 0; seg < 8; seg++)
        {
            data = 1 << seg;
            outb(~data, DATA_PORT); // turn on the segment
            // here we use inversion because the common anode 7-segment display is used
            sleep(1);
        }
    }

    ioperm(DATA_PORT, 1, 0); // release the port
}