Issues accessing arrays in Unity

Question

I'm trying to make a mini quiz game, but I'm stuck. I'm showing questions, randomly, but the first question never comes up. Furthermore, when I set the size of the questionsNumberChoosen array to 10 and run the game, it crashes.

public struct Question
{
    public string questionText;
    public string[] answers;
    public int correctAnswerIndex;

    // .. we also construct the Question, directly providing all values.
}

public Text questionText;
public Button[] answerButtons;

private Question currentQuestion;
private Question[] questions = new Question[10];
private int[] questionNumbersChoosen = new int[9];
private int questionsFinished;

void Start () 
{       
    questions [0] = new Question("1", new string[]{"A", "A", "A", "A", "A" }, 2);
    questions [1] = new Question("2", new string[]{"A", "A", "A", "A", "A" }, 0);
    questions [2] = new Question("3", new string[]{"A", "A", "A", "A", "A" }, 4);
    questions [3] = new Question("4", new string[]{"A", "A", "A", "A", "A" }, 0);
    questions [4] = new Question("5", new string[]{"A", "A", "A", "A", "A" }, 0);
    questions [5] = new Question("6", new string[]{"A", "A", "A", "A", "A" }, 2);
    questions [6] = new Question("7", new string[]{"A", "A", "A", "A", "A" }, 0);
    questions [7] = new Question("8", new string[]{"A", "A", "A", "A", "A" }, 4);
    questions [8] = new Question("9", new string[]{"A", "A", "A", "A", "A" }, 0);
    questions [9] = new Question("10", new string[]{"A", "A", "A", "A", "A" }, 0);

    setQuestionIndex ();
    assignQuestion (questionNumbersChoosen[0]);
}

void assignQuestion(int questionNum)
{
    currentQuestion = questions [questionNum];
    questionText.text = currentQuestion.questionText;
    for (int i=0; i < answerButtons.Length; i++)            
        answerButtons[i].GetComponentInChildren<Text>().text 
            = currentQuestion.answers [i];
}

public void checkAnswer(int buttonNum)
{
    if (buttonNum == currentQuestion.correctAnswerIndex) 
        print ("Correct!");
    else
        print ("Incorrect!");

    if (questionsFinished < (questionNumbersChoosen.Length - 1))        
        moveToNextQuestion ();
}

void setQuestionIndex()
{
    for (int i = 0; i < questionNumbersChoosen.Length; i++) 
    {
        int questionNum = Random.Range (0, questions.Length);

        if (!isContain (questionNumbersChoosen, questionNum))
            questionNumbersChoosen [i] = questionNum;
        else
            i--;
    }

}

bool isContain (int[] num, int numbers)
{
    for (int i=0; i < num.Length; i++) 
    {
        if (numbers == num [i])
            return true;            
    }

    return false;
}

public void moveToNextQuestion()
{
    assignQuestion (questionNumbersChoosen
        [questionNumbersChoosen.Length -1 - questionsFinished++]);
}

Answer 1

You could potentially be causing problems by editing the iterator in your for loop setQuestionIndex().

Try doing it without, like:

void setQuestionIndex()
{
    int questionIterator = 0;
    for (int i = 0; i < questionNumbersChoosen.Length; i++) {
         int questionNum = Random.Range (0, questions.Length);
         if (!isContain (questionNumbersChoosen, questionNum))
         {
              questionNumbersChoosen [questionIterator ] = questionNum;
              questionIterator ++;
         }
     }
}

Answer 2

You initialize the size of questionNumbersChoosen to length of 9 (or 10), and the values default to 0.

That means that anytime you randomly select question[0], isContain(questionNumbersChoosen, questionNum) is true, which is considered a failure.

When the length of questionNumbersChoosen is 10, and 9 questions have been assigned, the only question left to choose from is question[0], butquestion[0]keeps being rejected sincequestionNumbersChoosen[9]` is still the default value of 0.

The quickest fix is to initialize questionNumbersChoosen[] to a value outside of the range 0 to 9.

Answer 3

Though I do not see precisely what the specific problem is, I will list the few things that bother me in your code, and how you can easily find the bug yourself :

1. The loop in setQuestionIndex() method is error-prone and I suggest you fix it, as changing the iterator inside the loop is a bad practice imho. An option would be to do as Raeles suggests, replacing the for loop by a while (see my comment below his answer). An other option would just be to do some random permutations in your question array, which should prove more efficient.
2. I do not see where you initialize questionsFinished to 0. Maybe in Unity it is not mandatory to initialize variables, but still a good practice would be to explicitely write questionsFinished = 0 in your start method.
3. You do not need to pass questionNumbersChoosen in the parameters of isContain as it is a class variable. That just makes the code more confusing.

Now how would I debug it if I were you? In most IDE you can easily debug your code by adding Breakpoints. Just check step by step what is happening, put one in your setQuestionIndex loop to see if you have an infinite loop there (as you said Unity is freezing), if not just keep going, see how the questions are ordered in your array, check the state of the variables, and you should understand the problem pretty quickly.