In computing, C (//, as in the letter C) is a general-purpose programming language initially developed by Dennis Ritchie between 1969 and 1973 at AT&T Bell Labs. Like most imperative languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion, while a static type system prevents many unintended operations. C program source code is free-format, using the semicolon as a statement terminator and curly braces for grouping blocks of statements. Its design provides constructs that map efficiently to typical machine instructions, and therefore it has found lasting use in applications that had formerly been coded in assembly language, most notably system software like the Unix computer operating system.
C is one of the most widely used programming languages of all time, and there are very few computer architectures for which a Ccompiler does not exist.
Before there was an official standard for C, many users and implementors relied on an informal specification contained in a book byDennis Ritchie and Brian Kernighan; that version is generally referred to as "K&R" C. In 1989 the American National Standards Institutepublished a standard for C (generally called "ANSI C" or "C89"). The next year, the same specification was approved by theInternational Organization for Standardization as an international standard (generally called "C90"). ISO later released an extension to the internationalization support of the standard in 1995, and a revised standard (known as "C99") in 1999. The current version of the standard (now known as "C11") was approved in December 2011.