Introduction To C Language
The C language was invented at Bell Labs by Dennis Ritchie in 1972 to allow the writing of the UNIX operating system, then developed by Ken Thompson and Dennis Ritchie. The UNIX operating system, born in the late 1960s, was written directly in assembly language for the machines which it was intended. born in the late 1960s – early 1970s, was written directly in assembly language for the machines which it was intended. If the assembly language for writing such a system, it was nevertheless not easy to use. Such language is in fact a particular type of processor, which makes the whole system should be rewritten to make it work on a new architecture. This is its main creator, Ken Thompson, wanted to use a language more quickly evolved to rewrite UNIX.
Among the languages available at the time, BCPL (Basic Combined Programming Language for, which is a simplification of CPL), created by Martin Richards in 1966, was interesting. Without going into detailed descriptions, BCPL is a simple language, procedural, and not typed. Its simplicity makes it easy to create BCPL compilers on machines of the time, when resources were very limited (the first computer used by Keith Thompson was to launch a Unix PDP-7, which had a memory of 4000 words 18 bits, or less than 9 KB). Ken Thompson has evolved to design the B language, which he implemented the first UNIX machines. However, some limitations of language B were UNIX could be rewritten in this language.
From 1971, Dennis Ritchie B did evolve to address these issues. Like the programmers increment versions of their programs, Ritchie “Nudge” the letter B to call the new language C. This evolution is “stabilized” to 1973, from which UNIX and UNIX system utilities have been rewritten successfully in C language.
Subsequently in 1978, Brian W. Kernighan documentation very active language, and finally publish the book with reference Ritchie The C Programming Language. Often called K & R C language as specified in the first edition of this book.
In the years that followed, the C language was carried on many other machines. These ports were often made at the beginning, from the pcc compiler Steve Johnson, but then the original compilers were developed independently. During these years, every C compiler was written in accordance with the specifications of K & R, but some added extensions, such as data types or additional features, or different interpretations of certain parts of the book (not necessarily very precise). Because of this, it was less easy to write C programs that can run unchanged on many architectures.
C keywords are all lowercase, since uppercase and lowercase characters are not equivalent it’s possible to utilize an uppercase keyword as an identifier but it’s not a good programming practice.
Points to remember
1. Keywords can be used only for their intended purpose.
2. Keywords can’t be used as programmer defined identifier.
3. The keywords can’t be used as names for variables.
The standard keywords are given below: