int SetCurSel( int nSelect );
nSelect
Specifies the zero-based index of the string to select. If -1, any current selection in the list box is removed and the edit control is cleared.
Selects a string in the list box of a combo box. If necessary, the list box scrolls the string into view (if the list box is visible). The text in the edit control of the combo box is changed to reflect the new selection. Any previous selection in the list box is removed.
The zero-based index of the item selected if the message is successful. The return value is CB_ERR if nSelect is greater than the number of items in the list or if nSelect is set to -1, which clears the selection.
CComboBox::GetCurSel, CB_SETCURSEL