#include <avr/io.h>
#include <util/delay.h>

#define SegOne   0x01
#define SegTwo   0x02
#define SegThree 0x04
#define SegFour  0x08



int main() {
    char seg_code[]={0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90,0x88,0x83,0xc6,0xa1,0x86,0x8e};
    int cnt, num, temp,i;

    /* Configure the ports as output */
    DDRB = 0xff; // Data lines
    DDRD = 0xff; // Control signal PORTD0-PORTD3

    while (1)
    {
        for (cnt = 0x00; cnt <= 9999; cnt++) // loop to display 0-9999
        {
            for (i = 0; i < 100; i++)
            {
                num = cnt;
                temp = num / 1000;
                num = num % 1000;
                PORTD = SegOne;
                PORTB = seg_code[temp];
                _delay_ms(1);

                temp = num / 100;
                num = num % 100;
                PORTD = SegTwo;
                PORTB = seg_code[temp];
                _delay_ms(1);

                temp = num / 10;
                PORTD = SegThree;
                PORTB = seg_code[temp];
                _delay_ms(1);

                temp = num % 10;
                PORTD = SegFour;
                PORTB = seg_code[temp];
                _delay_ms(1);
            }
        }
    }
}