传递信息有困难

我在为学校做的一个程序中似乎遇到了一点障碍。我想做一个新的类来接收数据，并得到一个总发送到一个新的屏幕。我做了和课堂上一样的事情，但不同的是，那是一个文本框而这次我需要移动的数据没有文本框，所以我尝试的方式给了我一个错误。以下是我目前得到的结果:

    public StudentSelection()
    {
        InitializeComponent();
    }
    public decimal firstCounter;
    public decimal secondCounter;
    public decimal finalCounter;
    struct StudentScores
    {
        public string StuId;
        public decimal TestOne;
        public decimal TestTwo;
        public decimal Final;  
    }
    StudentScores[] allStudentScores = new StudentScores[10]; 
    // class level array to hold 10 products - read in from a file
    private void StudentSelection_Load(object sender, EventArgs e)
    {
        // read products file into products structure array
        try
        {

            // ALWAYS initialize a structure array before using the array
            //  before adding, changing, etc.
            for (int x = 0; x < 10; x++)
            {
                allStudentScores[x].StuId = "";
                allStudentScores[x].TestOne = 0;
                allStudentScores[x].TestTwo = 0;
                allStudentScores[x].Final = 0;
            }
            int arrayIndex = 0; // needed for incrementing index value of the array
            // when reading file into array
            // now read file into the array after initialization
            StreamReader inputFile;
            string lineofdata; // used to hold each line of data read in from the file
            string[] ProductStringArray = new string[4]; // 6 element string array to hold 
            // each "field" read from every line in file
            inputFile = File.OpenText("StudentScores.txt"); // open for reading
            while (!inputFile.EndOfStream) //keep reading until end of file
            {
                lineofdata = inputFile.ReadLine(); // ReadLine() reads an entire row of data from file
                ProductStringArray = lineofdata.Split(','); //each field is separated by ';'
                allStudentScores[arrayIndex].StuId = ProductStringArray[0]; // add first element of array to first column of allProducts
                allStudentScores[arrayIndex].TestOne = decimal.Parse(ProductStringArray[1]);
                firstCounter += allStudentScores[arrayIndex].TestOne;
                allStudentScores[arrayIndex].TestTwo = decimal.Parse(ProductStringArray[2]);
                secondCounter += allStudentScores[arrayIndex].TestTwo;
                allStudentScores[arrayIndex].Final = decimal.Parse(ProductStringArray[3]);
                finalCounter += allStudentScores[arrayIndex].Final;
                StudentListView.Items.Add(ProductStringArray[0]);
                arrayIndex++; // increment so NEXT row is updated with next read
            }
            //close the file
            inputFile.Close(); 
        }
        catch (Exception anError)
        {
            MessageBox.Show(anError.Message);
        }
    }
    private void NextButton_Click(object sender, EventArgs e)
    {
        decimal firstResult, secondResult, finalResult, stuOne, stuTwo, stuThree;
        string stuName;
        // call the method in our datatier class
        decimal.TryParse(firstCounter, out firstResult);
        decimal.TryParse(secondCounter, out secondResult);
        decimal.TryParse(finalCounter, out finalResult);
        DataTier.AddOurNumbers(firstResult, secondResult, finalResult);
        DataTier.StudentData(stuName, stuOne, stuTwo, stuThree);
        // now hide this window and display a third window with the total
        this.Hide();
        // display third window
        ScoreScreen aScoreScreen = new ScoreScreen();
        aScoreScreen.Show();
    }

}

和我的新类

class DataTier
{
    // public static variable available to all windows
    public static decimal firstTotal, secondTotal, finalTotal, stuTestOne, stuTestTwo, stuTestThree;
    // static is not associated with any object
    public static string stuIDCode;
    // create a public method to access from all windows
    public static void AddOurNumbers(decimal NumOne, decimal NumTwo, decimal numThree)
    {
        // devide to get an average
        firstTotal = NumOne / 10;
        secondTotal = NumTwo / 10;
        finalTotal = numThree / 10;
    }
    public static void StudentData(string name, decimal testOne, decimal testTwo, decimal testThree)
    {
        stuIDCode = name;
        stuTestOne = testOne;
        stuTestTwo = testTwo;
        stuTestThree = testThree;
    }
}

错误在小数点后三位。TryParse部分，我不知道为什么它不工作，除了错误说"不能从十进制转换为字符串"。