EN_CHANGE

This code specifies that the user has taken an action that may have altered text. It is sent after Windows updates a display (unlike the EN_UPDATE code). The control's parent window receives this code through a WM_COMMAND message from the control.

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_CHANGE code in its high-order word.