#include <CtrlLib/CtrlLib.h>

using namespace Upp;

struct MyAppWindow : TopWindow {
	Option option;
	MyAppWindow()
	{
		Sizeable().Zoomable().CenterScreen().SetRect(0,0, 640, 480);
		Add(option.SetLabel("Option").LeftPosZ(20).TopPosZ(20));
		option << [=] { Title(Format("Option (checbox) state: %", ~option)); };

		// OR,
		// option.WhenAction = [=] { Title(Format("Option (checbox) state: %", ~option)); };
	};
};

GUI_APP_MAIN
{
	MyAppWindow().Run();
}

bool IsChecked();     // value == 1
bool IsUnchecked()    // value == 0
bool IsInderminate(); // value == Null

    Option a;
    ....
    a = 1;  // set checked
    a = 0;  // set unchecked
    a = true;  // set checked
    a = false; // set unchecked
    a = !a;  // change checked
    ....
    if(a) // checked
    {
     ...
    }