int counter = 0;

void setup() {
  pinMode(10, OUTPUT);
  digitalWrite(10, LOW);
  Serial.begin(9600);
  Serial.println("Enter the first number you would like to multiply:");
  while (Serial.available() == 0) {}  
  String teststr = Serial.readString();
  int a = teststr.toInt();  
  Serial.println("Enter the second number you would like to multiply:");
  while (Serial.available() == 0) {}  
  String teststr2 = Serial.readString();  
  int b = teststr2.toInt();    

  Serial.println("Your two numbers multiplied together are:");
  int ans = multiply(a,b);
}

int multiply(int a, int b) {
  const int answer = a * b;
  Serial.println(answer);
  blink(answer);
}

void blink(int number){ //blinks led number of times answer gives
  if (counter < 1) {
    for (int i = 0; i < number; i++) {
      digitalWrite(10, HIGH);
      delay(500);
      digitalWrite(10, LOW);
      delay(500);
    }
    counter++;
  }
  else {
    digitalWrite(10, LOW);
  }
}

void loop() {

}