Introduction to C language
A Brief History of C
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.
Features of C language
• C is a case sensitive language
• C is a Middle level language
• C was invented to write an operating system called UNIX.
• C is a successor of B language which was introduced around the early 1970s.
• The language was formalized in 1988 by the American National Standard Institute (ANSI).
• The UNIX OS was totally written in C.
• Today C is the most widely used and popular System Programming Language.
• Most of the state-of-the-art software have been implemented using C.
• Today’s most popular Linux OS and RDBMS MySQL have been written in C.
IDENTIFIERS AND KEYWORDS
Identifiers
Identifiers are basically names given to program elements such as variables, arrays, and functions. They are formed by using a sequence of letters (both uppercase and lowercase), numerals, and underscores.
Following are the rules for forming identifier names
2. There cannot be two successive underscores.
3. Keywords cannot be used as identifiers.
4. The case of alphabetic characters that form the identifier name is significant. For example, ‘FIRST’ is different from ‘first’ and ‘First’.
6. Identifiers can be of any reasonable length. They should not contain more than 31 characters. (They can actually be longer than 31, but the compiler looks at only the first 31 characters of the name.)
Keywords
Like every computer language, C has a set of reserved words often known as keywords that cannot be used as an identifier. All keywords are basically a sequence of characters that have a fixed meaning. By convention, all keywords must be written in lower case letters. Table 1.1 contains the list of keywords in C.
| auto | break | case | char | const | continue | default | do |
| double | else | enum | extern | float | for | goto | if |
| int | long | register | return | short | signed | sizeof | static |
| struct | switch | typedef | union | unsigned | void | volatile | while |
