This message is sent by an application to set the check state of a radio button or check box.
BM_SETCHECK wParam = (WPARAM) fCheck, lParam = 0;
Specifies the check state. It is one of the following values.
Sets the button state to checked.
Sets the button state to grayed, indicating an indeterminate state. Use this value only if the button has the BS_3STATE or BS_AUTO3STATE style.
Sets the button state to unchecked.