If you add this after everything has been completed (all marks have been entered and converted) then it will work (obviously rename the controls or variables as you need).
vb Code:
  1. Me.Label1.Text = String.Empty
  2.  
  3.         For i As Integer = 0 To charGrade.Length - 1
  4.  
  5.             Me.Label1.Text &= charGrade(i) & Environment.NewLine
  6.  
  7.         Next