Private Type UserData
    Username As String * 30
    Password As String * 30
End Type

Private Sub Command1_Click()
    Dim FileIn As Integer
    Dim CurrentUser As UserData, CheckUser As UserData
    FileIn = FreeFile
    Open App.Path & "\users.txt" For Random As #FileIn Len = Len(CheckUser)
   
    CurrentUser.Username = Text1.Text
    CurrentUser.Password = Text2.Text
   
    Do While Not EOF(FileIn)
        Get #FileIn, , CheckUser
        If CurrentUser.Username = CheckUser.Username And CurrentUser.Password = CheckUser.Password Then
            MsgBox "Successfully Logged In"
            Close #FileIn
            Exit Sub
        End If
    Loop
   
    MsgBox "Unsuccessfully Logged In"
    Close #FileIn
End Sub

Private Sub Command2_Click()
    Dim FileOut As Integer
    Dim SaveUser As UserData
    FileOut = FreeFile
    Open App.Path & "\users.txt" For Random As #FileOut Len = Len(SaveUser)
   
    SaveUser.Username = Text1.Text
    SaveUser.Password = Text2.Text
   
    Put #FileOut, LOF(FileOut) / Len(SaveUser) + 1, SaveUser    'Append userdata to file
   
    MsgBox "Successfully Registered"
    Close #FileOut
End Sub