Objective-C

Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. It was the main programming language supported by Apple for macOS, iOS, and their respective application programming interfaces (APIs), Cocoa and Cocoa Touch, until the introduction of Swift in 2014.

The language was originally developed in the early 1980s. It was later selected as the main language used by NeXT for its NeXTSTEP operating system, from which macOS and iOS are derived. Portable Objective-C programs that do not use Apple libraries, or those using parts that may be ported or reimplemented for other systems, can also be compiled for any system supported by GNU Compiler Collection (GCC) or Clang.

Objective-C source code 'implementation' program files usually have .m filename extensions, while Objective-C 'header/interface' files have .h extensions, the same as C header files. Objective-C++ files are denoted with a .mm file extension.