#include <Keypad.h>  // Correct capitalization

const uint8_t ROWS = 4;  // 4 rows
const uint8_t COLS = 4;  // 4 columns

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};  // Connect to C1, C2, C3, C4
uint8_t rowPins[ROWS] = {9, 8, 7, 6};  // Connect to R1, R2, R3, R4

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

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

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

  if (key != NO_KEY) {
    Serial.print(key);
  }
}