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• C Programming Tutorial
• C Programming useful Resources

• Selected Reading

You have seen the basic structure of a C program, so it will be easy to understand other basic building blocks of the C programming language.

Tokens in C

Techsatish mallu. A C program consists of various tokens and a token is either a keyword, an identifier, a constant, a string literal, or a symbol. For example, the following C statement consists of five tokens −

The individual tokens are −

Semicolons

In a C program, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.

Given below are two different statements −

Comments

Comments are like helping text in your C program and they are ignored by the compiler. They start with /* and terminate with the characters */ as shown below −

You cannot have comments within comments and they do not occur within a string or character literals.

Identifiers

A C identifier is a name used to identify a variable, function, or any other user-defined item. An identifier starts with a letter A to Z, a to z, or an underscore '_' followed by zero or more letters, underscores, and digits (0 to 9).

C does not allow punctuation characters such as @, $, and % within identifiers. C is a case-sensitive programming language. Thus, Manpower and manpower are two different identifiers in C. Here are some examples of acceptable identifiers −

Keywords

The following list shows the reserved words in C. These reserved words may not be used as constants or variables or any other identifier names.

Whitespace in C

A line containing only whitespace, possibly with a comment, is known as a blank line, and a C compiler totally ignores it.

Whitespace is the term used in C to describe blanks, tabs, newline characters and comments. Whitespace separates one part of a statement from another and enables the compiler to identify where one element in a statement, such as int, ends and the next element begins. Therefore, in the following statement −

there must be at least one whitespace character (usually a space) between int and age for the compiler to be able to distinguish them. On the other hand, in the following statement −

no whitespace characters are necessary between fruit and =, or between = and apples, although you are free to include some if you wish to increase readability.

• C Programming Tutorial
• C Programming useful Resources

• Selected Reading

C is a general-purpose, high-level language that was originally developed by Dennis M. Ritchie to develop the UNIX operating system at Bell Labs. C was originally first implemented on the DEC PDP-11 computer in 1972.

In 1978, Brian Kernighan and Dennis Ritchie produced the first publicly available description of C, now known as the K&R standard.

The UNIX operating system, the C compiler, and essentially all UNIX application programs have been written in C. C has now become a widely used professional language for various reasons −

• Easy to learn
• Structured language
• It produces efficient programs
• It can handle low-level activities
• It can be compiled on a variety of computer platforms

Facts about C

• 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.

Why use C?

C was initially used for system development work, particularly the programs that make-up the operating system. C was adopted as a system development language because it produces code that runs nearly as fast as the code written in assembly language. Some examples of the use of C might be −

• Operating Systems
• Language Compilers
• Assemblers
• Text Editors
• Print Spoolers
• Network Drivers
• Modern Programs
• Databases
• Language Interpreters
• Utilities

C Programs

A C program can vary from 3 lines to millions of lines and it should be written into one or more text files with extension '.c'; for example, hello.c. You can use 'vi', 'vim' or any other text editor to write your C program into a file.

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This tutorial assumes that you know how to edit a text file and how to write source code inside a program file.