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

int i = 0;
int j = 0;
LiquidCrystal_I2C mylcd(0x27,16,2);

const byte rows = 4;
const byte cols = 4;

char key[rows][cols] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'#', '0', '*', 'D'} // '#' is now the clear key, '*' is the result key
};

byte rowPins[rows] = {9, 8, 7, 6};
byte colPins[cols] = {5, 4, 3, 2};

Keypad keypad = Keypad(makeKeymap(key), rowPins, colPins, rows, cols);

// Variables to store calculator input and result
String inputString = "";
float result = 0.0;

void setup() {
  mylcd.init();
  mylcd.clear();         
  mylcd.backlight(); 
  mylcd.setCursor(0, 0);
  mylcd.print("Calculator:");
  mylcd.setCursor(0, 1);
}

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

  if (press != NO_KEY) {
    if (press == 'A') { // Addition
      inputString += '+';
    } else if (press == 'B') { // Subtraction
      inputString += '-';
    } else if (press == 'C') { // Multiplication
      inputString += '*';
    } else if (press == 'D') { // Division
      inputString += '/';
    } else if (press == '#') { // Clear the entire input
      inputString = "";
    } else if (press == '*') { // Calculate and display result
      // Check if the input is not empty
      if (inputString.length() > 0) {
        result = calculateResult(inputString);
        mylcd.setCursor(0, 1);
        mylcd.print("Result:       ");
        mylcd.setCursor(8, 1);
        mylcd.print(result);
        delay(2000); // Delay to display the result before clearing
        inputString = "";
        mylcd.setCursor(0, 1);
        mylcd.print("             "); // Clear the result
      }
    } else { // Numeric and other characters
      inputString += press;
    }

    // Display the input string
    mylcd.setCursor(0, 1);
    mylcd.print("             "); // Clear the previous input
    mylcd.setCursor(0, 1);
    mylcd.print(inputString);
  }
}

float calculateResult(String input) {
  // Implement the calculation here
  // This example assumes a simple calculation with one operator
  int operatorPos = -1;

  // Find the position of an operator character
  for (int i = 0; i < input.length(); i++) {
    if (input.charAt(i) == '+' || input.charAt(i) == '-' ||
        input.charAt(i) == '*' || input.charAt(i) == '/') {
      operatorPos = i;
      break;
    }
  }

  if (operatorPos == -1 || operatorPos == 0 || operatorPos == input.length() - 1) {
    return 0.0; // Invalid input or no operator
  }

  float num1 = input.substring(0, operatorPos).toFloat();
  float num2 = input.substring(operatorPos + 1).toFloat();
  char op = input.charAt(operatorPos);

  switch (op) {
    case '+':
      return num1 + num2;
    case '-':
      return num1 - num2;
    case '*':
      return num1 * num2;
    case '/':
      if (num2 != 0.0) {
        return num1 / num2;
      } else {
        return 0.0; // Division by zero
      }
    default:
      return 0.0; // Invalid operator
  }
}