Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.It was selected as the main language used by NeXT for its NeXTSTEP operating system, from which macOS and iOS are derived.
Object Oriented Programming + Structured Programming = Objective C
Objective-C is the primary language used to write Mac software.
Objective-C® is a superset of the ANSI version of the C programming language and supports the same basic syntax as C.
Everything C can do, Objective-C can do too, but not the other way around.
All the object oriented syntax and operations are derived from SmallTalk.
All the non-object oriented syntax and operations are identical to C.
Since it lies on top of C, it is possible to compile any C program with an Objective-C compiler, and to freely include C code within an Objective-C class.
Objects, Classes, and Messaging
Defining a Class
Allocating and Initializing Objects
Categories and Extensions
Enabling Static Behavior