#include <Keypad.h>

// Define the dimensions of the keypad
const byte ROWS = 4; // four rows
const byte COLS = 4; // four columns

// Define the keymap
char keys[ROWS][COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '*'},
  {'*', '0', '#', '/'}
};

// Define the row and column pins
byte rowPins[ROWS] = {2, 3, 4, 5}; // Connect to the row pins of the keypad
byte colPins[COLS] = {6, 7, 8, 9}; // Connect to the column pins of the keypad

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

void setup() {
  // Start the Serial communication
  Serial.begin(9600);
}

void loop() {
  int num1 = -1;
  int num2 = -1;
  char operation = 0;
  int result = 0;
  bool validOperation = true;

  // Start the operation cycle
  Serial.println("Press '*' to start a new operation.");

  // Wait for the user to press '@'
  int flag = 1;
  while (true) {
    char startKey = keypad.getKey();
    if (startKey == '*') {
      Serial.println("Starting new operation...");
      break;
    }
  }

  // Get the first number
  Serial.print("ENTER THE FIRST NUMBER: ");
  while (num1 == -1) {
    char key = keypad.getKey();
    if (key >= '0' && key <= '9') {
      num1 = key - '0'; // Convert character to integer
      Serial.println(num1);
    }
  }

  // Get the second number
  Serial.print("ENTER THE SECOND NUMBER: ");
  while (num2 == -1) {
    char key = keypad.getKey();
    if (key >= '0' && key <= '9') {
      num2 = key - '0'; // Convert character to integer
      Serial.println(num2);
    }
  }

  // Get the operation
  Serial.println("Operations: + = addition, - = subtraction, * = multiplication, / = division");
  Serial.print("ENTER THE OPERATION: ");
  while (operation == 0) {
    operation = keypad.getKey();
    if (operation == '+' || operation == '-' || operation == '*' || operation == '/') {
      Serial.println(operation);
    }
  }

  // Perform the operation
  if (operation == '+') {
    result = num1 + num2;
  } else if (operation == '-') {
    result = num1 - num2;
  } else if (operation == '*') {
    result = num1 * num2;
  } else if (operation == '/') {
    if (num2 != 0) {
      result = num1 / num2;
    } else {
      Serial.println("Error: Division by zero!");
      validOperation = false;
    }
  } else {
    validOperation = false;
    Serial.println("Invalid operation!");
  }

  // Output the result if the operation was valid
  if (validOperation) {
    Serial.print("Result: ");
    Serial.print(num1);
    Serial.print(" ");
    Serial.print(operation);
    Serial.print(" ");
    Serial.print(num2);
    Serial.print(" = ");
    Serial.println(result);
  }

  // Wait for the user to press '#' before starting a new operation
  Serial.println("Operation complete. Press '#' to start again.");
  while (true) {
    char endKey = keypad.getKey();
    if (endKey == '#') {
      Serial.println("Restarting...");
      break;
    }
  }
}