C was invented and first implemented by Dennis Ritchie on a DEC PDP-11 that used the UNIX operating system. C is the result of a development process that started with an older language called BCPL. BCPL was developed by Martin Richards, and it influenced a language called B, which was invented by Ken Thompson. B led to the development of C in the 1970s. For many years, the de facto standard for C was the version supplied with the UNIX operating system. It was first described in The C Programming Language by Brian Kernighan and Dennis Ritchie (Englewood Cliffs, N.J.: Prentice-Hall, 1978). In the summer of 1983 a committee was established to create an ANSI (American National Standards Institute) standard that would define the C language. The standardization process took six years (much longer than anyone reasonably expected at the time). The ANSI C standard was finally adopted in December of 1989, with the first copies becoming available in early 1990. The standard was also adopted by ISO (International Standards Organization) and the resulting standard was typically referred to as ANSI/ ISO Standard C. In 1995, Amendment 1 to the C standard was adopted, which, among other things, added several new library functions. The 1989 standard for C, along with Amendment 1, became the base document for Standard C++, defining the C subset of C++. The version of C defined by the 1989 standard is commonly referred to as C89. After 1989, C++ took center stage, and during the 1990s the development of a standard for C++ consumed most programmers’ attention, with a standard for C++ being adopted by the end of 1998. However, work on C continued along quietly. The end result was the 1999 standard for C, usually referred to as C99. In general, C99 retained nearly all of the features of C89 and did not alter the main aspects of the language. Thus, the C language described by C99 is essentially the same as the one described by C89. The C99 standardization committee focused on two main areas: the addition of several numeric libraries and the development of some special-use, but highly innovative, new features, such as variable- length arrays and the restrict pointer qualifier. In a few cases, features originally from C++, such as single-line comments, were also incorporated into C99. Because the standard for C++ was finalized before C99 was created, none of the C99 innovations are found in Standard C++.