4. Key words

There are certain reserved words, called keywords, which have standard, predefined meanings in C.

These keywords can be used only for their intended purpose; they cannot be used as programmer-defined identifiers.

Some standard keywords are:

auto extern sizeof break floatn static case for char

switch register return long int else while short void

Some C compilers may recognize other keywords.

Note that the keywords are all lowercase. Since uppercase and lowercase characters are not equivalent, it is possible to utilize an uppercase keyword as an identifier.

Normally, however, this is not done, as it is considered a poor programming practice.

3. Identifiers

Identifiers are names that are given to various program elements, such as variable, functions and arrays.

Identifiers consist of letters and digits, in any order, except that the first character must be a letter.;

Both upper- and lowercase letters are permitted, though common usage favors the use of lowercase letters for most types of identifiers. Upper- and lowercase letters are not interchangeable.

The underscore (_) character can also be included, and is considered to be a letter. An underscore is often used in the middle of an identifier.

An identifier may also begin with an underscore, though this is rarely done in practice.

The following names are valid identifiers:

x y12 sum_1 tax_rate area _temperature

2. The C character set

C uses the uppercase letter A to Z, the lowercase letters a to z, the digits 0 to 9, and certain special characters as building blocks to form basic program elements ( e.g., constants, variables, operators, expressions, etc.).

Some of the special characters are listed below:

+ - * ~ % / & ( ) { } [ ] ? " < > ! ; :

Most versions of the language also allow certain other characters, such as @ and $, to be included within strings and comments.

C uses certain combinations of these characters, such as \b,\n and \t, to represent special conditions such as backspace, new line, and horizontal tab, respectively

These character combinations are known as escape sequences.

1. Introduction

C language consists of some basic elements which are used to construct simple C statements.

These elements include the C character set, identifiers, and keywords, data types, constants, variables and arrays, declaration, expressions and statements.

We will see how these basic elements can be combined to form more comprehensive program components.