Adding grades to a text file in vb.net

Question

Hello I'm trying to add new grades to a text file using the button btnRECORD entered in the textbox txtRECORD. I'm using the button btnDISPLAY to calculate the average of the grades and the number of grades above average and display them in a listbox. But I can't seem to add new grades to the textfile with btnRECORD. (the textfile is empty)

  Public Class frmGRADES
Dim temp() As String = IO.File.ReadAllLines("Exam.txt")
Dim grades(temp.Length - 1) As Double
Dim average As Double
Dim aboveAverage As Integer

Function avg(ByVal average As Double, ByVal aboveAverage As Integer)//function for average
    For i As Double = 0 To grades.Length - 1
        If grades(i) > average Then
            aboveAverage = aboveAverage + 1
        End If
    Next
    Return aboveAverage
End Function

Private Sub btnRECORD_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRECORD.Click
    ReDim Preserve grades(temp.Length - 1)
    grades(temp.Length - 1) = CDbl(txtRECORD.Text)
    IO.File.WriteAllLines("Exam.txt", grades) //write grades to textfile
    aboveAverage = 0
End Sub

Private Sub btnDISPLAY_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDISPLAY.Click
    lstRESULTS.Items.Clear()
    For i As Integer = 0 To grades.Length - 1
        grades(i) = CDbl(temp(i))
    Next
    average = grades.Average
    lstRESULTS.Items.Add("The Average Score is: " & average)
    aboveAverage = avg(average, aboveAverage)


    lstRESULTS.Items.Add("Number of Grades above average is: " & aboveAverage)
    aboveAverage = 0
End Sub
End Class

Answer 1

Oops your C# is showing :). Comments in VB are signified with a '

Your main problem appears to be casting an array of double to string. In the WriteAllLines method. Something like this should work better:

    IO.File.WriteAllLines("Exam.txt", (From d In grades
                                             Let str As String = d.ToString
                                             Select str).ToArray)

Another thing I noticed, array indexes are integer but one of your for loops is declared with a double.

To use the return type of a function you should explicitly declare that type so that the compiler can recognize it.

 Function avg(ByVal average As Double, ByVal aboveAverage As Integer) As Integer