#include <Keypad.h>

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

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

bool distInput = false;
char dist[3] = "";
byte index = 0;
int targetDistance = 0;

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

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

  switch (key)
  {
    case '0' ... '9':
      if (distInput == true)
      {
        Serial.print(key);
        if (index < 2)
        {
          dist[index] = key;
          dist[index + 1] = '\0';
          index++;
        }
        if (index == 2)
        {
          targetDistance = atoi(dist);

          if ((targetDistance < 50) && (targetDistance > 2))
          {
            index = 0;
            memset(dist, 0, 2); // Clear input
            distInput = false;
            Serial.print("\nYour target distance is:");
            Serial.print(targetDistance);
            Serial.println(" cm.");
            distInput = false;
          }
          else if (targetDistance < 3)
          {
            index = 0;
            memset(dist, 0, 2); // Clear input
            distInput = false;
            Serial.println("\nThe minimum distance is 03 cm.");
          }
          else
          {
            index = 0;
            memset(dist, 0, 2); // Clear input
            distInput = false;
            Serial.println("\nThe maximum distance is 49 cm.");
          }
        }
      }
      break;
    case '*':
      if (distInput == false)
      {
        Serial.println("\nPlease input Target value 03-49 cm (2 digits).");
        distInput = true;
      }
      break;
    case '#':
      if (distInput == false)
      {
        Serial.println("\nEnd of measurement.");     // for the case of pressing a '#'
      }
      break;
    default:
      break;
  }
}