Subscript Out of Range

I am trying to write a program in VBA to calculate GPA.

The form has a listbox to slect grades and a textbox for users to enter the credits.

I need to store the grades in an array once btnrecord is clicked and once user clicks BtnCalculate, I want to calculate the GPA and display the result in another textbox.

I am getting "Subscript out of range error" in the array with the following code.

Private Sub btnRecord_Click()
    
   Dim x As Long
      Dim temparray() As Variant
      
       If (IsNumeric(TextBox1.Text) = False) Then
        MsgBox "You must enter an integer number"
    Exit Sub
    End If
     
    ReDim temparray(1 To TextBox1.Text)
     
     
     For I = 1 To TextBox1.Text
     
        
            Select Case Me.ListBox1.Value
                Case "A+"
                    temparray(x) = (4.33 * n)
                Case "A"
                    temparray(x) = (4 * n)
               Case "A-"
                    temparray(x) = (3.67 * n)
                Case "B+"
                    temparray(x) = (3.33 * n)
               Case "B"
                    temparray(x) = (3 * n)
               Case "B"
                   temparray(x) = (2.67 * n)
               Case "C+"
                    temparray(x) = (2.33 * n)
                Case "C"
                    temparray(x) = (2 * n)
               Case "C-"
                   temparray(x) = (1.67 * n)
                Case "D+"
                    temparray(x) = (1.33 * n)
                Case "D"
                    temparray(x) = (1 * n)
               Case "D-"
                   temparray(x) = (0.67 * n)
           End Select
        
      Next I
ReDim Preserve temparray(x)
    
End Sub

Please help.

Thanks,
Blyzzard

I am not sure about how many courses will be there in each trancript, so cannot set the upperbound.