Why I can't increment in scala?

Question

  def guessing_game():Unit = {
    println("Welcome to the guessing game!!")

    val guess_count:Int = 0
    val answer = Random.nextInt(50)
    var guess_num = scala.io.StdIn.readLine("Input your guess number > ").toInt

    while(guess_num != answer || guess_count < 5){

 ====> guess_count += 1    //  <==============================

      var situation = if(guess_num > answer){"Your guess is higher!"}else{"Your guess is lower!"}
      println(situation)
      guess_num = scala.io.StdIn.readLine("Input your guess number > ").toInt
    }
    if(guess_num == answer){
      println("Congratulation....You win!!")
    }else{
      println("You hav run out of guess!")
    }

I get this error:

Error:(16, 25) value += is not a member of Int

Expression does not convert to assignment because receiver is not assignable.
guess_count.toInt += 1

Answer 1

guess_count is immutable, (val), you cannot change it. Use var if you need to change the variable.