Private Sub chia(ByVal tb1 As MSForms.TextBox, ByVal tb2 As MSForms.TextBox, ByVal lb As MSForms.Label)
If Not IsNumeric(tb1.Value) Then
lb.Caption = "Loi so chia"
MsgBox ("Nhap lai so chia")
tb1 = ""
ElseIf Not IsNumeric(tb2.Value) Or tb2.Value = 0 Then...