const int numRows = 4;
const int numCols = 4;

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

/*bool arrayRows[numRows][numCols] =
  {
  {0, 1, 1, 1},
  {1, 0, 1, 1},
  {1, 1, 0, 1},
  {1, 1, 1, 0},
  };*/

// connect to the row pinouts of the keypad
int rowPins[numRows] = {9, 8, 7, 6};

// connect to the column pinouts of the keypad
int colPins[numCols] = {5, 4, 3, 2};


void setup()
{
  Serial.begin(9600);
}


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

  if (key != 0)
  {
    Serial.println(key);
    delay(100);
  }
}


char getKey()
{
  for (int row = 0; row < numRows; ++row)
  {
    pinMode(rowPins[row], OUTPUT);
    digitalWrite(rowPins[row], LOW);

    for (int col = 0; col < numCols; ++col)
    {
      pinMode(colPins[col], INPUT_PULLUP);

      if (digitalRead(colPins[col]) == LOW)
      {
        delay(50); // Debounce
        while (digitalRead(colPins[col]) == LOW)
        {} // Wait for key release
        return keymap[row][col];
      }

      pinMode(colPins[col], INPUT); // Set column pin back to input
    }

    pinMode(rowPins[row], INPUT); // Set row pin back to input
  }

  return 0; // Return 0 if no key is pressed
}