int num1, num2;
char operation;

void setup() {
  Serial.begin(9600);
  while (!Serial); // Wait for Serial to start
  Serial.println("=== Simple Serial Calculator ===");
}

void loop() {
  // ASK first number
  Serial.println("Enter first number: ");
  while (Serial.available() == 0);  // WAIT
  num1 = Serial.parseInt();        // READ
  Serial.read(); // clear buffer

  // ASK second number
  Serial.println("Enter second number: ");
  while (Serial.available() == 0);  // WAIT
  num2 = Serial.parseInt();        // READ
  Serial.read(); // clear buffer

  // ASK operation
  Serial.println("Enter operation (+, -, *, /): ");
  while (Serial.available() == 0);  // WAIT
  operation = Serial.read();       // READ

  // Perform calculation
  Serial.print("Result: ");
  switch (operation) {
    case '+':
      Serial.println(num1 + num2);
      break;
    case '-':
      Serial.println(num1 - num2);
      break;
    case '*':
      Serial.println(num1 * num2);
      break;
    case '/':
      if (num2 != 0) {
        Serial.println((float)num1 / num2);
      } else {
        Serial.println("Error! Division by zero.");
      }
      break;
    default:
      Serial.println("Invalid operation.");
      break;
  }

  // Serial.println("-----------------------------");
  // delay(500); // Small pause before restarting
}