Option Explicit

Private Sub cmdVer_Click()
    Dim inf As Long, sup As Long, k As Long
    Dim aux As Long, num As Long
    lstNP.Clear
    
    inf = Val(txtLI.Text)
    sup = Val(txtLS.Text)
    If sup < inf Then
        aux = inf
        inf = sup
        sup = aux
    End If
    
    If inf <= 0 Then
        MsgBox "Os limites estão errados!"
        Exit Sub
    End If
    
    For num = inf To sup
        k = 2
        Do While k <= num \ 2 And num Mod k <> 0
            k = k + 1
        Loop
        If k > num / 2 Then
            lstNP.AddItem num
        End If
    Next
End Sub