Basic thing: Objective-C type and constant

Several data types in objective-C are not the same as those in C. It is hereby recorded.

-ID is a pointer type that can point to any type of object.

-Bool is the same as char, but it is used as a Boolean value.

Yes indicates 1

No indicates 0

-Iboutlet is a macro without any meaning and can be ignored. When interface builder reads class definitions from. H files, this macro will prompt them.

-The ibaction and void are the same. They are only used as prompts for interface builder.

-Nil is the same as null. We use nil instead of null because we use it to indicate that the object pointer is null.

 

In addition

# Import is the same as # include, but # import ensures that the Referenced File is referenced only once.

From: http://www.cocoachina.com/newbie/basic/2009/0611/50.html