#include <GUIConstantsEx.au3>

Local $hGUI = GUICreate("Обучалка алфавиту", 300, 200)
Local $alf = "абвгдеёжзийклмнопрсткфхцчшщъыьэюя"
local $counter = 0
Local $idButton = GUICtrlCreateButton("Следующая буква", 100, 170, 100, 25)
Local $letter = GUICtrlCreateLabel("", 110, 30,100,100)
GUICtrlSetFont($letter,25)
GUISetState(@SW_SHOW, $hGUI)

While 1
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE
ExitLoop
Case $idButton
$counter  = $counter +1
if ($counter > 33) then $counter = 1
$sym = StringMid($alf, $counter,1)

GUICtrlSetData($letter,$sym)

EndSwitch
WEnd