What values should I use for iOS boolean states?

Question

It appears that in iOS I have a number of options that seem to fit for boolean values:

YES
NO
TRUE
FALSE
true
false

Which ones should I use

Answer 1

I think all of them are okay. But personally, I'd like to use YES/NO.

I found a doc called Objective-C Runtime Reference:

Boolean Values These macros define convenient constants to represent Boolean values.

#define YES (BOOL)1
#define NO (BOOL)0

Constants

YES
Defines YES as 1.
Available in iOS 2.0 and later.
Declared in NSObjCRuntime.h.

NO
Defines NO as 0.
Available in iOS 2.0 and later.
Declared in NSObjCRuntime.h.

Declared In
objc.h