tristate check box

I have a tristate check box.The default behavour of tristate check box in windows is that, the grayed check box will become unchecked after click on grayed check box.

But i want , the grayed check box will become checked after click on grayed check box in VC++ .Pls help me its urgent.

 

just declare a bool val to that checkbox and intialize it to 1 int the InitDilaog method;