void init_port()
{
  volatile char *ddrf = (char *)0x30;   // DDRF – data direction for rows
  volatile char *ddrk = (char *)0x107;  // DDRK – data direction for columns
  volatile char *portk = (char *)0x108; // PORTK – to enable pull-ups
volatile char *ddra=(char *)0x21;
volatile char *ddrd=(char *)0x2A;
  *ddrf = 0x0F;   // Lower 4 bits as output (rows)
  *ddrk = 0x00;   // All PORTK pins as input (columns)
  *portk = 0xFF;  // Enable pull-ups
  *ddra=0x0FF;
  *ddrd=0xFF;
}


char output(char data)
{
  volatile char *pout= (char *)0x31;
  *pout=data;
  
}

char input()
{
  volatile char *pinK = (char *)0x106;  // PIN register for PORTK
  char input_d = ~(*pinK);              // Invert since active low
  return input_d;
}


int keymap[4][4] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7','8','9', 'C'},
  {'*', '0','#','D'}
};

char getkeyr() {
  int row, col;
  char value;

  for (row = 0; row < 4; row++) {
    output(~(1 << row));  // Make one row low at a time (active low)
    delay(1);             // Small delay for signal stabilization
    value = input();
    
    if (value != 0x00) {  // A key was pressed in this row
      for (col = 0; col < 4; col++) {
        if (value & (1 << col)) {
          // Return the mapped key
          delay(200);  // Debounce delay
          return keymap[row][col];
        }
      }
    }
  }
  return 0;  // No key press detected
}


void setup() {
  init_port();
  Serial.begin(9600);
  Serial.println("choose option after entering values");
Serial.println("A : ADDITION");
Serial.println("B : SUBTRACTION");
Serial.println("C : MULTIPLICATION");
Serial.println("D : DIVISION");

Serial.println("# : clear inputs");

Serial.println("range : <=9999 ");
}

volatile char *portd = (char *)0x2B;
volatile char *porta = (char *)0x22;


int seg_pattern[10] = {
  0x3F, // 0
  0x06, // 1
  0x5B, // 2
  0x4F, // 3
  0x66, // 4
  0x6D, // 5
  0x7D, // 6
  0x07, // 7
  0x7F, // 8
  0x6F  // 9
};

void out(char x)
{
    volatile char *out;
    out = 0x2B;
    *out = 0x0F;
    out = 0X22;
    x=0x00;
    *out = x;
}








int count = 0;
char digits[8] = {' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '};
char operation = ' ';
bool showResult = false;

void loop() {
  char key = getkeyr();

  if (key >= '0' && key <= '9' && count < 8) {
    digits[count++] = key;
    delay(200);
  }

  // Wait for operation key after 8 digits are entered
  if (count == 8 && (key == 'A' || key == 'B' || key == 'C' || key == 'D')) {
    operation = key;
    
    int num1 = (digits[0] - '0') * 1000 + (digits[1] - '0') * 100 +
               (digits[2] - '0') * 10 + (digits[3] - '0');
    int num2 = (digits[4] - '0') * 1000 + (digits[5] - '0') * 100 +
               (digits[6] - '0') * 10 + (digits[7] - '0');
    int result = 0;

    switch (operation) {
      case 'A': result = num1 + num2; break;
      case 'B': result = num1 - num2; break;
      case 'C': result = num1 * num2; break;
      case 'D': result = (num2 != 0) ? num1 / num2 : 0; break;
    }
    Serial.println(operation);

    // Display only 4 digits of result
    digits[0] = (result / 1000) % 10 + '0';
    digits[1] = (result / 100) % 10 + '0';
    digits[2] = (result / 10) % 10 + '0';
    digits[3] = result % 10 + '0';
    showResult = true;
    delay(500);
  }

  // Reset system with '#' key
  if (key == '#') {
    count = 0;
    showResult = false;
    operation = ' ';
    for (int i = 0; i < 8; i++) digits[i] = ' ';
    delay(300);
  }

  // Display logic
  for (int i = 0; i < 4; i++) {
    char val = showResult ? digits[i] : (count <= 4 ? digits[i] : digits[i + 4]);

    if (val >= '0' && val <= '9') {
      *porta = seg_pattern[val - '0'];
    } else {
      *porta = 0x00;
    }

    switch (i) {
      case 0: *portd = 0x0E; break;
      case 1: *portd = 0x0D; break;
      case 2: *portd = 0x0B; break;
      case 3: *portd = 0x07; break;
    }

    delay(5);
    *portd = 0xFF;
  }
}