Private intX As Integer
Private charGrade(30) As Char
Private strMark As String
Private intTotal, intMax As Integer
Private intStudents As Integer
Private dblpercent As Double
Private strGrade As String

Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click

intStudents = (Convert.ToInt32(txtNumberOfStudents.Text))
INTMAX = (Convert.ToInt32(txtCourseMarks.Text))
For intX = 0 To (intStudents - 1)

intX = Convert.ToInt32(InputBox("Please enter the students mark"))
intTotal = intTotal + intX


dblpercent = Convert.ToInt32(strMark) / 100 * intMax


If Me.radDay.Checked Then

If dblpercent >= 90 Then
strGrade = "A"
ElseIf dblpercent >= 80 Then
strGrade = "B"
ElseIf dblpercent >= 70 Then
strGrade = "C"
ElseIf dblpercent >= 60 Then
strGrade = "D"
ElseIf dblpercent < 60 Then
strGrade = "F"
End If

Else
If dblpercent >= 85 Then
strGrade = "A"
ElseIf dblpercent >= 75 Then
strGrade = "B"
ElseIf dblpercent >= 65 Then
strGrade = "C"
ElseIf dblpercent >= 50 Then
strGrade = "D"
ElseIf dblpercent < 50 Then
strGrade = "F"
End If
End If

charGrade(intX) = (Convert.ToChar(strGrade))


Next
For intX = 0 To intStudents - 1
Label3.Text = Label3.Text & charGrade(intX).ToString & ControlChars.NewLine
Next
End Sub
End Class

THE INPUT BOX LINE AND LINE BELOW IT KEEP MAKING MY CODE STOP COULD ANY 1 PLZ OFFER ME SOME HELP
THANKS