Public Class Form1

 Dim textoAnterior As String
    Dim labelAnterior As String
    Dim charcase As CharacterCasing
    Private Sub btnMayus_Click(sender As Object, e As EventArgs) Handles btnMayus.Click

        textoAnterior = TextBox1.Text
        labelAnterior = Label2.Text
        charcase = TextBox1.CharacterCasing


        TextBox1.Text = TextBox1.Text.ToUpper
        TextBox1.CharacterCasing = CharacterCasing.Upper
        Label2.Text = "El texto está en modo mayúsculas"
        Label2.ForeColor = Color.Red

    End Sub

    Private Sub btnMinus_Click(sender As Object, e As EventArgs) Handles btnMinus.Click
        textoAnterior = TextBox1.Text
        labelAnterior = Label2.Text
        charcase = TextBox1.CharacterCasing
        TextBox1.Text = TextBox1.Text.ToLower
        TextBox1.CharacterCasing = CharacterCasing.Lower

        Label2.Text = "El texto está en modo minúsculas"
        Label2.ForeColor = Color.Red

    End Sub

    Private Sub btnPwd_Click(sender As Object, e As EventArgs) Handles btnPwd.Click
        textoAnterior = TextBox1.Text
        labelAnterior = Label2.Text
        charcase = TextBox1.CharacterCasing
        TextBox1.PasswordChar = "*"
        Label2.Text = "El texto está en modo Contraseña"
        Label2.ForeColor = Color.Red
        TextBox1.CharacterCasing = CharacterCasing.Normal

    End Sub

    Private Sub btnNormal_Click(sender As Object, e As EventArgs) Handles btnNormal.Click
        textoAnterior = TextBox1.Text
        labelAnterior = Label2.Text
        charcase = TextBox1.CharacterCasing
        If TextBox1.PasswordChar = "*" Then TextBox1.PasswordChar = ""
        TextBox1.CharacterCasing = CharacterCasing.Normal
        Label2.Text = "El texto está en modo Normal"
        Label2.ForeColor = Color.Red

    End Sub

    Private Sub btnSelMayus_Click(sender As Object, e As EventArgs) Handles btnSelMayus.Click
        If String.IsNullOrWhiteSpace(TextBox1.SelectedText) Then
            MessageBox.Show("No hay texto seleccionado")
            Exit Sub
        End If
        textoAnterior = TextBox1.Text
        labelAnterior = Label2.Text
        charcase = TextBox1.CharacterCasing
        TextBox1.CharacterCasing = CharacterCasing.Normal
        TextBox1.SelectedText = TextBox1.SelectedText.ToUpper

        Label2.Text = "El texto seleccionado está en Mayúsculas"
        Label2.ForeColor = Color.Red

    End Sub

    Private Sub btnMinusculas_Click(sender As Object, e As EventArgs) Handles btnMinusculas.Click
        If String.IsNullOrWhiteSpace(TextBox1.SelectedText) Then
            MessageBox.Show("No hay texto seleccionado")
            Exit Sub
        End If
        textoAnterior = TextBox1.Text
        labelAnterior = Label2.Text
        charcase = TextBox1.CharacterCasing
        TextBox1.CharacterCasing = CharacterCasing.Normal
        TextBox1.SelectedText = TextBox1.SelectedText.ToLower

        Label2.Text = "El texto seleccionado está en Minúsculas"
        Label2.ForeColor = Color.Red

    End Sub

    Private Sub btnSalir_Click(sender As Object, e As EventArgs) Handles btnSalir.Click
        Close()
    End Sub

    Private Sub btnUndo_Click(sender As Object, e As EventArgs) Handles btnUndo.Click
        If TextBox1.PasswordChar = "*" Then TextBox1.PasswordChar = ""
        TextBox1.CharacterCasing = charcase
        TextBox1.Text = textoAnterior
        Label2.Text = labelAnterior

    End Sub
End Class