The PBM_STEPIT message advances the current position for a progress bar by the step increment and redraws the bar to reflect the new position. An application sets the step increment by sending the PBM_SETSTEP message.
PBM_STEPIT wParam = 0; lParam = 0;
Returns the previous position.
When the position exceeds the maximum range value, this message resets the current position so that the progress indicator starts over again from the beginning.