iOS how can i refer both class's variable?

[junmoney83]

There is two class

First, Second.h


first.h
<-------
#import"second.h"
@interface:first
@end


second.h
@class first.h;
@interface:first
@end


i want to refer each class's variable.
but there is an error which message is " Accessing unKnown '~~~' component of a property"
when set first's variable at second class.

how can i solve this problem?

and i have other question. if i want to see list of my question.
what do i do?