C is a general-purpose, structured programming language. Structured Languages have a characteristic program structure and associated set of static scope rules (static scope rules are discussed in detail later). The structured programming concepts originated in the language ALGOL 60, one of the most important early languages. They have been adopted in other languages because of their elegance and effect on implementation efficiency. In a structured or to be more specific Block-structured language, each program or subprogram is organised as a set of nested blocks. The chief characteristic of a block is that it introduces a new local referencing environment. A block begins with a set of declarations for names (variable declarations, type definitions, constant definitions, etc.), followed by a set of statements in which those names may be referenced. In C, there is a block structure, but it exists only within a single subprogram.
C was originally developed in the 1970’s by Dennis Ritchie at Bell Telephone Laboratories, Inc. (now AT&T Bell Laboratories). In 1978, Brian Kernighan and Ritchie published a comprehensive description of the language C. The Kernighan and Ritchie description is commonly referred to as “K&R C”. Following the publication of the K & R description, computer professionals, impressed with C’s many desirable features, began to promote the use of the language. Since 1980’s, the popularity of C has become widespread. Most commercial implementations of C differ somewhat from Kernighan and Ritchie’s original definition. This has created some incompatibilities among different implementations of the language, thereby diminishing the portability of the application program developed using C. Consequently, the American National Standards Institute (ANSI) proposed a standardised definition of the C language (ANSI committee X3J11). Most commercial C compilers and interpreters are expected to adopt the ANSI standard.
The statements in C resemble other high-level programming languages such as Pascal and FORTRAN-77. C also supports certain additional features, that allow it to be used at a lower level, thus bridging the gap between machine language and the more conventional high-level languages. This flexibility allows C to be used for systems programming (e.g., for writing operating systems) as well as for applications programming (e.g., for scientific computation, mathematical equations, or for business data processing).
It is possible to develop concise source programs in C mainly due to the large number of operators available in the language. Although the language has a relatively small instruction set, it is possible to include extensive library functions that enhance the basic instructions. Furthermore, the language encourages users to write additional library functions of their own. Thus, the features and capabilities of the language can easily be extended by the user.
C compilers are available for all types of computers ranging from PCs, workstations to super computers. The compilers are usually highly optimised, and generate object programs that are small and efficient. In addition, C programs are highly portable, as compared to the programs written in other high-level languages. The reason for this is that machine dependent features are often handled by library functions. Thus, every version of C is accompanied by its own set of library functions, which are written for the particular characteristics of the host computer. These library functions are relatively standardised with a common access protocol for these functions. Therefore, most C programs can be processed on different machines with little or no alteration.