Mikael Olsson - Modern C Quick Syntax Reference: A Pocket Guide to the Language, APIs, and Library

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The C programming language is a general-purpose, middle-level language originally developed by Dennis M. Ritchie at Bell Labs. It was created over the period 1969 through 1973 for the development of the UNIX operating system, which had previously been written in assembly language. The name C was chosen because many of its features derived from an earlier language called B. Whereas the B language is no longer in common use, C became and still remains one of the most popular and influential programming languages in use today.

Although C is a general-purpose language, it is most often used for systems programming. This includes software that controls the computer hardware directly, such as drivers, operating systems, and software for embedded microprocessors. C can also be used for writing applications, which run on top of system software. However, it has largely been superseded in that domain by higher-level languages, such as C++, Objective-C, C#, and Java. The features of these and many other languages are heavily influenced by C, as can be seen in some of their names.

The development of C was a major milestone in computer science, as it was the first widely successful middle-level language for system development. The foremost reasons for its success were that the language was concise, fast, and powerful. It offered comparable speed to assembly with far improved usability. The high-level constructs of the language allowed programmers to focus mainly on the softwares design, while its low-level capabilities still provided direct access to the hardware when needed, as assembly had done. Furthermore, the language is relatively simple to understand, with few keywords and what many consider to be an elegant syntax.

Another major reason for the success of C was its portability. Unlike assembly, the C language is platform independent. A standards-compliant C program can therefore be compiled for a wide variety of computer systems with few changes to its source code. Moreover, the C compiler was small and easy to port to different CPU architectures, which together with the languages popularity has made C compilers available on most computer systems.

In 1978, Brian Kernighan and Dennis Ritchie produced the first publicly available description of C, now known as K&R C. This description was succeeded in 1989 when the American National Standards Institute (ANSI) provided a comprehensive definition of C known as ANSI C or C89. In the following year, the same specification was adopted as an international standard by the International Organization for Standardization and became known as ISO C90 or just C90. C has since undergone four more revisions by ISO (successively adopted by ANSI) with further language extensions, including C95, C99, C11, and most recently C18, which is the latest ANSI standard for the C programming language. The current C18 standard provided only clarifications to C11 and introduced no new language features.