Hi Graham,

Are you wedded to clunky old CString?
Basically - I do a lot with MFC.

Below is probably more helpful...
Code:
CString s;
CryptoPP::Integer n;
s << n;
SetEditWindowText( IDC_EDIT_MODULUS, n );
Then,
Code:
VOID SetEditWindowText( UINT nID, const CString& szText ) {
	CEdit* pEdit = static_cast<CEdit*>( GetDlgItem( nID ) );
	if( NULL != pEdit ) { pEdit->SetWindowText( szText ); }
}
Jeff