Stop modalpopup until i click yes or no

dear sir

I have created a messagebox using the ajax modalpopup
But when i show the modalpopup i want it to stay and do not execute the code which are written after the line where i am using modalpopup.show();

And when user click yes or no on the modalpopup it executes the line afterward bcos the input which user gives on that modalpopup decides what to do next

Thanks please reply