const uint8_t ROWS = 4;
const uint8_t COLS = 4;
char keys[ROWS][COLS] = {
  { '1', '2', '3', 'A' },
  { '4', '5', '6', 'B' },
  { '7', '8', '9', 'C' },
  { '*', '0', '#', 'D' }
};

uint8_t colPins[COLS] = { 5, 4, 3, 2 }; // Pins connected to C1, C2, C3, C4
uint8_t rowPins[ROWS] = { 9, 8, 7, 6 }; // Pins connected to R1, R2, R3, R4


void setup() {
  Serial.begin(9600);
    // Set row pins as INPUT_PULLUP and column pins as OUTPUT (initially LOW)
 init_kaypad();

 int aa = map(50,10,20,100,200);
 Serial.println(aa);
}

void loop() {
 loop_keypad();
}


void init_kaypad() {
  // Set row pins as INPUT_PULLUP and column pins as OUTPUT (initially LOW)
  for (byte i = 0; i < ROWS; i++) {
    pinMode(rowPins[i], INPUT_PULLUP);
  }
  for (byte i = 0; i < COLS; i++) {
    pinMode(colPins[i], OUTPUT);
    digitalWrite(colPins[i], LOW);
  }
}


void loop_keypad() {
  static uint32_t prev = 0;
  char pressedKey = getKey();
  if (pressedKey == '\0') { // '\0' indicates no key pressed
    return;
  }
  if (millis() - prev < 500) { // debounce it
    return;
  }
  prev = millis();
  Serial.print("pressed: ");
  Serial.println(pressedKey);
}


char getKey() {
  for (int col = 0; col < COLS; col++) {
    digitalWrite(colPins[col], HIGH); // Activate current column

    for (int row = 0; row < ROWS; row++) {
      if (digitalRead(rowPins[row]) == LOW) { // Check if a row is pulled low (key pressed)
        digitalWrite(colPins[col], LOW); // Deactivate current column before returning
        return keys[row][col];
      }
    }
    digitalWrite(colPins[col], LOW); // Deactivate current column
  }
  return '\0'; // No key pressed
}