Calculator in VB

Public curval As Double
Public preval As Double
Public choice As String
Public result As Double

Private Sub cmdac_Click()
curval = prevalue = 0
Text1.Text = ""

End Sub

Private Sub cmddiv_Click()
Text1.Text = ""
preval = curval
curval = 0
choice = "/"

End Sub

Private Sub cmdequal_Click()
Select Case choice
Case "+"
result = preval + curval
Text1.Text = Str(result)

Case "-"
result = preval - curval
Text1.Text = Str(result)

Case "*"
result = preval * curval
Text1.Text = Str(result)

Case "/"
If curval = 0 Then
MsgBox "Result is not defined"

Else
result = preval / curval
Text1.Text = Str(result)
End If


End Select
curval = result

End Sub

Private Sub cmdminus_Click()
Text1.Text = ""
preval = curval
curval = 0
choice = "-"

End Sub

Private Sub cmdmul_Click()
Text1.Text = ""
preval = curval
curval = 0
choice = "*"

End Sub

Private Sub cmdnegative_Click()
curval = -curval
Text1.Text = Str(curval)

End Sub

Private Sub cmdnos_Click(Index As Integer)


End Sub

Private Sub cmdplus_Click()
Text1.Text = ""
preval = curval
curval = 0
choice = "+"

End Sub

Private Sub Command1_Click(Index As Integer)
Text1.Text = Text1.Text & Command1(Index).Caption
curval = Val(Text1.Text)
End Sub