if(!IsPostback) doesn't exist in the current context

Question

I'm building a web application using a webform and I'm trying to store a counter in a Session, but I'm getting the error that if(!IsPostback) doesn't exist in the current context. Can anyone help me with this issue?

protected void Page_Load(object sender, EventArgs e)
{
        if(!IsPostback)
{
Session["AttemptCount"] = 0;
}

}

  protected void submitAnswerButton_Click(object sender, EventArgs e)
    {



        //difficultyList.SelectedIndex = 2;
        answerStatus.Visible = true;


        int answer = randomNumber1 + randomNumber2;
        int counter = (int)Session["AttemptCount"];
        if (mathAnswerTextBox.Text == answer.ToString())
        {
  counter++;
            Session["AttemptCount"] = counter;

            answerStatus.Text = "Correct!";


           // scoreLabel.Text = "Score: " + counter.ToString();
            randomNumber1 = random.Next(0, 50);
            randomNumber2 = random.Next(0, 50);
            num1Label.Text = Convert.ToString(randomNumber1);//add this line 
            num2Label.Text = Convert.ToString(randomNumber2); //and this line
            num1Label.Visible = true;
            num2Label.Visible = true;
            mathAnswerTextBox.Visible = true;

            submitAnswerButton.Visible = true;
        }
        else if (mathAnswerTextBox.Text != answer.ToString())
        {

            answerStatus.Text = "Incorrect";

            incorrectStrikes.Text = counter.ToString();
            num1Label.Visible = true;
            num2Label.Visible = true;
            mathAnswerTextBox.Visible = true;
            submitAnswerButton.Visible = true;
        //    scoreLabel.Text = counterArray[0].ToString();

        }

Answer 1

As I previously mentioned in my comment to your question, your original problem was with the lowercase b in Postback. The reason your "AttemptCount" session variable is not being incremented is because your if statement only increments it:

if (mathAnswerTextBox.Text == answer.ToString())

I think you want to do this in the else clause of your if statement, and not when the answer is correct.