IF EXIST "*a_*" GOTO :SIHAY
ELSE GOTO :NOHAY

IF EXIST "*a_*" (
    GOTO :SIHAY
) ELSE (
    GOTO :NOHAY
)

"(CUALQUIER_SERIE_DE_CARACTERES)a_(CUALQUIER_SERIE_DE_CARACTERES)"

IF EXIST "*?_*" (Echo Si hay coincidencias) ELSE (Echo No hay coincidencias)

IF EXIST "???????????????_????????????"  (Echo Si hay coincidencias) ELSE (Echo No hay coincidencias)

Imports System.Windows.Forms
Imports System.IO
Imports System.Text.RegularExpressions
 
Public Class Form1
    Dim filesystem As Object, ThisDir As Object
    Dim mcheck(0) As CheckBox
    Dim winampargs As String

#Region "Propertys"
    Public Property userSelectedPlayerFilePath() As String
        Get
            Return playertextbox.Text
        End Get
        Set(value As String)
            playertextbox.Text = value
        End Set
    End Property
 
    Public Property userSelectedFolderPath() As String
        Get
            Return foldertextbox.Text
        End Get
        Set(value As String)
            foldertextbox.Text = value
        End Set
    End Property
#End Region

#Region "Load / Close"
 
    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        playertextbox.Text = My.Settings.playerpath
        foldertextbox.Text = My.Settings.folderpath
        updatecheckboxes()
    End Sub
 
    Private Sub Form1_FormClosing(sender As Object, e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        Dim mCheckados(0) As Int32
        Dim Cuantos As Int32 = 0
        For i As Int32 = 0 To mcheck.Length - 1
            If mcheck(i).Checked = True Then
                Cuantos += 1
                Array.Resize(mCheckados, Cuantos)
                mCheckados(Cuantos - 1) = i + 1
            End If
        Next
        My.Settings.Valores = mCheckados
        My.Settings.Save()
    End Sub
 
#End Region

#Region "Save & Get settings"
 
    Public Sub GenerarPropiedades()
        Dim CheckedN As String = Nothing
        For i As Int32 = 0 To mcheck.Length - 1
            If mcheck(i).Checked = True Then
                CheckedN &= i + 1
            End If
        Next
        My.Settings.Save()
    End Sub
 
    Private Sub CargarPropiedades()
        'Obtenemos la Lista de Enteros de los índices Checkados
        Dim ListaCheckados As Int32() = My.Settings.Valores
        For i As Int32 = 0 To mcheck.Length - 1
            For Each indiceCheckado As Int32 In ListaCheckados
                mcheck(indiceCheckado - 1).Checked = True
            Next
        Next
    End Sub
 
#End Region

#Region "Draw checkboxes..."
 
    Public Sub updatecheckboxes()
        ' delete the old checkboxes
        Panel1.Controls.Clear()
        ' create the new checkboxes
        Dim filesystem = CreateObject("Scripting.FileSystemObject")
        Dim ThisDir = filesystem.GetFolder(My.Settings.folderpath)
        Dim i As Int32 = 0
        For Each folder In ThisDir.Subfolders
            Array.Resize(mcheck, i + 1)
            mcheck(i) = New CheckBox
            With mcheck(i)
                .AutoSize = True
                .Location = New Point(10, i * 20)
                .Name = "CheckBox" & i + 1
                .Text = folder.Name
            End With
            Me.Panel1.Controls.Add(mcheck(i))
            AddHandler mcheck(i).CheckedChanged, AddressOf LlamadaCheckBox
            i += 1
        Next
        CargarPropiedades()
    End Sub
 
    ' función que se ejecuta cuando cualquier checkbox es clickado
    Public Sub LlamadaCheckBox(ByVal sender As Object, ByVal e As System.EventArgs)
        Dim filesystem = CreateObject("Scripting.FileSystemObject")
        Dim ThisDir = filesystem.GetFolder(My.Settings.folderpath)
        Dim CheckboxN As CheckBox = CType(sender, CheckBox)
        If CheckboxN.Checked = True Then
            winampargs = winampargs & " " & ControlChars.Quote & Path.Combine(ThisDir.Path, CheckboxN.Text.ToString()) & ControlChars.Quote
        Else
            winampargs = Replace(winampargs, ControlChars.Quote & Path.Combine(ThisDir.Path, CheckboxN.Text.ToString()) & ControlChars.Quote, "")
        End If
    End Sub
 
#End Region

#Region "buttons"
 
    ' Folder button
    Public Sub C1Button3_Click(sender As Object, e As EventArgs) Handles folderbutton.Click
        Dim folderselected As New System.Windows.Forms.FolderBrowserDialog
        Dim Resultado As DialogResult
        folderselected.RootFolder = Environment.SpecialFolder.Desktop
        Resultado = folderselected.ShowDialog
        If Resultado.ToString() = "OK" Then
            userSelectedFolderPath = folderselected.SelectedPath
            My.Settings.folderpath = folderselected.SelectedPath
            My.Settings.Save()
            Dim mcheck(0) As CheckBox
            updatecheckboxes()
        End If
    End Sub
 
    ' Player button
    Public Sub C1Button1_Click(sender As Object, e As EventArgs) Handles playerbutton.Click
        Dim playerselected As New OpenFileDialog()
        playerselected.InitialDirectory = Environ("programfiles")
        playerselected.Title = "Select your favorite music player"
        playerselected.Filter = "Music players|mpc.exe;mpc-hc.exe;mpc-hc64.exe;umplayer.exe;vlc.exe;winamp.exe;wmp.exe"
        PlayerDialog.FilterIndex = 1
        Dim selection As System.Windows.Forms.DialogResult = playerselected.ShowDialog()
        If selection = DialogResult.OK Then
            userSelectedPlayerFilePath = playerselected.FileName
            My.Settings.playerpath = playerselected.FileName
            My.Settings.Save()
        End If
    End Sub
 
    ' Play button
    Public Sub C1Button2_Click(sender As Object, e As EventArgs) Handles C1Button2.Click
        Process.Start(userSelectedPlayerFilePath, winampargs)
    End Sub
 
#End Region

End Class

Dim ListaCheckados As Int32() = My.Settings.Valores

My.Settings.Valores = mCheckados

        <Global.System.Configuration.UserScopedSettingAttribute(), _
         Global.System.Diagnostics.DebuggerNonUserCodeAttribute(), _
         Global.System.Configuration.DefaultSettingValueAttribute("0")> _
        Public Property Valores() As Int32()
            Get
                Return CType(Me("Valores"), Int32())
            End Get
            Set(value As Int32())
                Me("Valores") = value
            End Set
        End Property
    End Class
End Namespace

Index was outside the bounds of the array. 

    Private Sub CargarPropiedades()
                mcheck(indiceCheckado - 1).Checked = True
    End Sub

    ' Folder button
    Public Sub C1Button3_Click(sender As Object, e As EventArgs) Handles folderbutton.Click
     ...
        If Resultado.ToString() = "OK" Then
            Dim mcheck(0) As CheckBox
            updatecheckboxes()

    ' update checkboxes
    Public Sub updatecheckboxes()
        ' delete the old checkboxes
        Panel1.Controls.Clear()
        ' create the new checkboxes
        Dim filesystem = CreateObject("Scripting.FileSystemObject")
        Dim ThisDir = filesystem.GetFolder(My.Settings.folderpath)
        Dim i As Int32 = 0
        For Each folder In ThisDir.Subfolders
            'MessageBox.Show("a")
            Array.Resize(mcheck, i + 1)
            mcheck(i) = New CheckBox
            With mcheck(i)
                .Name = "CheckBox" & i + 1
                '.Text = mcheck(i).Name
                .Text = folder.Name
                .Location = New Point(10, i * 20)
            End With
            Me.Panel1.Controls.Add(mcheck(i))
            AddHandler mcheck(i).CheckedChanged, AddressOf LlamadaCheckBox
            i += 1
        Next
        CargarPropiedades()
    End Sub