EN_VSCROLL

This code specifies that the user has clicked the edit control's vertical scroll bar. The control's parent window receives this code through a WM_COMMAND message from the control; notification occurs before the screen is updated.

Parameter Description  

wParam Contains the wParam parameter of the WM_COMMAND message, and specifies the control ID.  
lParam Contains an edit-control window handle in its low-order word and the EN_VSCROLL code in its high-order word.