What's wrong with this code?

[JwQuick]

It won't compile because of a "Use of unassigned local variable 'answer' "
Any help would be appreciated, and don't flame because I'm still a beginner.

        string theOperator;
        private void btnAnswer_Click(object sender, EventArgs e)
        {
            int firstTextBoxNumber = int.Parse(tbFirstNumber.Text);
            int secondTextBoxNumber = int.Parse(tbSecondNumber.Text);
            int answer;
            theOperator = tbOperatorSymbol.Text;

            switch (theOperator)
            {
                case "+":
                        answer = firstTextBoxNumber + secondTextBoxNumber;
                        break;
                case "-":
                        answer = firstTextBoxNumber - secondTextBoxNumber;
                        break;
                case "*":
                        answer = firstTextBoxNumber * secondTextBoxNumber;
                        break;
                case "/":
                        answer = firstTextBoxNumber / secondTextBoxNumber;
                        break;
                default:    
                        //Insert Code
                        break;
            }

            MessageBox.Show(answer.ToString());
        }