void CheckDlgButton( int nIDButton, UINT nCheck );
nIDButton
Specifies the button control to be modified.
nCheck
Specifies the action to take. If nCheck is nonzero, the CheckDlgButton member function places a check mark next to the button; if 0, the check mark is removed. For three-state buttons, if nCheck is 2, the button is dimmed; if nCheck is 1, it is checked; if nCheck is 0, the check mark is removed.
Places a check mark next to or removes a check mark from a button control, or, for a three-state button, may dim the button.
CWnd::IsDlgButtonChecked, ::CheckDlgButton