#include <SPI.h>
#include <Wire.h>
#include <Keypad.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
Adafruit_SSD1306 display = Adafruit_SSD1306(128, 64, &Wire);
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] = { 2, 0, 4, 16 }; // Pins connected to C1, C2, C3, C4
uint8_t rowPins[ROWS] = { 12, 14, 27, 26 }; // Pins connected to R1, R2, R3, R4

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

void setup() {
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3c); 
  display.clearDisplay();
  display.setTextColor(WHITE, BLACK); 
  display.setCursor(0,5);
  display.setTextSize(3);
}

void loop() {
  char key = keypad.getKey();
  if (key) {
  Serial.println(key);
  display.print(key);
  display.display();
  }
  delay(100);
  if (key == 'D')
   display.clearDisplay();
   display.display();
   display.setCursor(0,5);

  }