summing elements of a .txt file array in VB.net - arrays

Question

College student in an advanced VB class who is turning to a forum for help - I've found a few examples of code but am having a hard time figuring this one out.. any and all help is appreciated :)
This application imports a .txt file stored in the bin, debug folder called data.txt
..20 records, 3 lines per record, the last line is the student's grade, I need to average the grades by summing each records grade and dividing by 20 and then displaying on the lstbox showing the average.
So far I've got..
Dim objReader As IO.StreamReader
Dim intFill As Integer
Dim intCount As Integer = 0
Dim intAverage As Integer
Dim strLocationAndNameOfFile As String = "data.text"
If IO.File.Exists(strLocationAndNameOfFile) = True Then
objReader = IO.File.OpenText(strLocationAndNameOfFile)
Else
MsgBox("The file is not available. Restart the program when the file is avilable", , "Error")
Me.Close()
End If
If IO.File.Exists(strLocationAndNameOfFile) Then
objReader = IO.File.OpenText(strLocationAndNameOfFile)
Do While objReader.Peek <> -1
_strName(intCount) = Convert.ToString(objReader.ReadLine())
_strItemID(intCount) = Convert.ToString(objReader.ReadLine())
_intGrade(intCount) = Convert.ToInt32(objReader.ReadLine())
intCount += 1
Loop
objReader.Close()
End If
For intFill = 0 To (_strName.Length - 1)
*'intAverage = SUM OF ALL AVERAGES / LENGTH OF ARRAY -1*
Me.lstAverage.Items.Add(intAverage.ToString())

Answer 1

While looping to read the grades sum them up
Dim total as Integer
Do While objReader.Peek <> -1
_strName(intCount) = Convert.ToString(objReader.ReadLine())
_strItemID(intCount) = Convert.ToString(objReader.ReadLine())
_intGrade(intCount) = Convert.ToInt32(objReader.ReadLine())
total += _intGrade(intCount)
intCount += 1
Loop
And then just divide by 20 or _intGrade.Length
intAverage = total / _intGrade.Length

Answer 2

So many issues, as much as I loathe doing other's homework I want you to see what this could look like
Public Function GetAverageGrade(ByVal filename As String) As Double
Dim totalGrade As Integer = 0
Dim lineCount As Integer = 0
Dim line As String
Using rdr As New IO.StreamReader(filename)
While (line = rdr.ReadLine()) IsNot Nothing
lineCount += 1
If lineCount Mod 3 = 0 Then totalGrade += Convert.ToInt32(line)
End While
End Using
Return totalGrade / (lineCount / 3.0)
End Function
Of course, you probably want to do more with that data than just get the average grade. So an even better option is build code that reads it all in as a set of records:
Public Class GradeItem
Public Property Name As String
Public Property Item As String
Public Property Grade As Integer
End Class
and then
Public Iterator Function ReadGradeItems(ByVal fileName As String) As IEnumerable(Of GradeItem)
Using rdr As New IO.StreamReader(fileName)
While rdr.Peek() <> -1
Yield New GradeItem With {.Name = rdr.ReadLine(), .Item= rdr.ReadLine(), .Grade = Convert.ToInt32(rdr.ReadLine()}
End While
End Using
End Function
and now put it all together:
Dim grades As IEnumerable(Of GradeItem) = ReadGradeItems("data.text")
lstAverage.Items.Add(grades.Select(Function(g) g.Grade).Average())