#include <Arduino.h>

// Define registers (adjust these based on your hardware)
#define PORTF 0x30  // Output for the 7-segment display
#define PORTK 0x107 // Input for switches
#define OUTF 0x31   // Output register for PORTF
#define INK 0x106   // Input register for PORTK

const char ssd[10] = {0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F}; 

void setup() {
    *(volatile char*)PORTF = 0xFF; 
    *(volatile char*)PORTK = 0x00; 
}

void loop() {
    int digits[4] = {0, 0, 0, 0}; 
    int sum = 0;

    for (int i = 0; i < 4; i++) {
        bool digitEntered = false; 

        while (!digitEntered) {
            char switchState = *(volatile char*)INK; 
            for (int j = 0; j < 8; j++) {
                if (switchState & (1 << j)) { 
                    digits[i] = j; 
                    *(volatile char*)OUTF = ssd[j]; 
                    delay(1000); 
                    digitEntered = true; 
                    break;
                }
            }
        }
        while (*(volatile char*)INK > 0);
    }

    for (int i = 0; i < 4; i++) {
        sum += digits[i]; 
    }

    while (sum > 9) {
        int tempSum = 0;
        while (sum > 0) {
            tempSum += sum % 10;
            sum /= 10; 
        }
        sum = tempSum; 
    }

    *(volatile char*)OUTF = ssd[sum]; 
    delay(3000);

    *(volatile char*)OUTF = 0x00; 
    delay(500);
}