#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <Keypad.h>
#include <math.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);
const byte ROWS = 4;
const byte COLS = 3;
char keys[ROWS][COLS] = {
  {'1','2','3'},
  {'4','5','6'},
  {'7','8','9'},
  {'*','0','#'}
};
byte rowPins[ROWS] = {2, 4, 5, 16};
byte colPins[COLS] = {13, 14, 25};
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {
  Wire.begin();
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("Enter c (cm):");
}

void loop() {
  char key = keypad.getKey();
  
  if (key) {
    static char buffer[10];
    static int index = 0;
    
    if (key == '#') {
      buffer[index] = '\0';
      float circumference = atof(buffer);
      float radius = circumference / (2 * M_PI);
      float area = M_PI * pow(radius, 2);
      
      lcd.clear();
      lcd.setCursor(0, 0);
      lcd.print("Area: ");
      lcd.setCursor(6, 0);
      lcd.print(area);
      index = 0;
    } else {
      buffer[index++] = key;
      lcd.setCursor(index - 1, 1);
      lcd.print(key);
    }
  }
}