Tic Tac Toe

String board[] = {"","","","","","","","",""};

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

}

void loop() {
  // put your main code here, to run repeatedly:
  if(checkIfOver()) {
    resetBoard();
  }
  else {
    playerPlaceX();
  }
  if(checkIfOver()) {
    resetBoard();
  }
  else {
    HEROPlaceO();
  }
}

boolean isAvailable(int square) {
  if(board[square]==""){
    return true;
  }
  else {
    return false;
  }
}

void resetBoard() {
  Serial.println("Resetting board...");
  delay(5000);
  for(int i = 0; i < 8; i++){
    board[i] = "";
  }
}
void playerPlaceX() {
  Serial.println("Where would you like to place an X? Enter 0-8");
  while (Serial.available() == 0) { // stops program from continuing until Serial.available is 0, or the user inputs something.
     //wait for user to input data
  }
  int playerChoice = Serial.readString().toInt();

  if (isAvailable(playerChoice)) {
    board[playerChoice] = 'X';
  }
  else {
    Serial.println("Spot already contains: " + board[playerChoice]);
    delay(2000);
    playerPlaceX();
  }
}

void HEROPlaceO() {
  randomSeed(analogRead(0));
  int AIChoice = random(9);
  if(isAvailable(AIChoice)){
    board[AIChoice] = 'O';
    Serial.println("HERO Placed 0 in board spot " + String(AIChoice));
  }
  else {
    HEROPlaceO();
  }
}

boolean crossCheck(String a, String b, String c){
  if(a.equals(b) && b.equals(c)){
    if(c.equals("")){
      return false;
    }
    return true;
  }
  else {
    return false;
  }
}

boolean boardFull() {
  for(int i = 0; i < 8; i++){
    if(board[i].equals("")) {
      return false;
    }
  }
  return true;
}

boolean checkIfOver() {
  if(crossCheck(board[0], board[3], board[6])
  || crossCheck(board[0], board[1], board[2])
  || crossCheck(board[0], board[4], board[8])) { //case 1-3
    Serial.println(board[0] + " wins!");
    return true;
  }
  else if(crossCheck(board[4], board[3], board[5])
  || crossCheck(board[4], board[1], board[7])
  || crossCheck(board[4], board[2], board[6])) { //case 4-6
    Serial.println(board[4] + " wins!");
    return true;
  }
  else if(crossCheck(board[8], board[6], board[7])
  || crossCheck(board[8], board[2], board[5])) { //case 7-8
    Serial.println(board[8] + " wins!");
    return true;
  }
  else if(boardFull()) {
    Serial.println("A draw has occured.");
    return true;
  }
  else {
    return false;
  }
}