C Keywords & Identifiers
In this tutorial, you will learn about Character set, Keywords, Escape sequence characters and identifiers in C programming. We will also learn about rules for naming identifiers.
Character set
A character set is a set of uppercase and lowercase alphabets, digits, whitespaces and some special characters that are valid in C language.
Alphabets
Uppercase: A B C ................................... X Y Z
Lowercase: a b c ...................................... x y z
Digits
0 1 2 3 4 5 6 7 8 9
Special Characters
There are 29 special characters in C language.
| , | . | ; | : | # |
| " | ! | | | ~ | > |
| > | _ | $ | ( | ) |
| % | ? | & | ^ | * |
| - | + | [ | ] | { |
| } | / | \ | ' |
White space Characters
Blank space, newline, carriage return, horizontal tab, vertical tab and form feed.
Escape Sequence Characters
Escape sequence characters are used to perform special tasks to manage the C program. They are also known as backslash character constants.
| Character | Escape Sequence | ASCII value |
|---|---|---|
| bell (alert) | \a | 007 |
| backspace | \b | 008 |
| horizontal tab | \t | 009 |
| the new line (line feed) | \n | 010 |
| vertical tab | \v | 011 |
| form feed | \f | 012 |
| null | \0 | 000 |
| a quotation mark(") | \" | 034 |
| carriage return | \r | 013 |
| apostrophe(') | \' | 039 |
| a question mark(?) | \? | 063 |
| backslash(\b) | \\ | 092 |
| octal number | \o0 | Eg., \005, \123, \177 |
| hexadecimal number | \xhh | Eg., \x5, \x7f |
Keywords
Keywords are predefined, reserved words in C language that have special meanings to the compiler. We cannot use it as an identifier (variable name, constant name, etc). Keywords are part of the syntax. There are only 32 reserved words (keywords) in the C language.. For example:
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 |
Example :
int marks;In the above example, int is a keyword that indicates marks is a int
(integer) type variable .
Note : C is a case sensitive language and all keywords must be written in lowercase. So, we don't use keywords as identifiers.
To know more about all these keywords click - List of all keywords in C programming.
Identifiers
Identifier is the user-defined word used to represent programming entities such as variables, functions, structures, unions etc.
Identifier are used to identify an entity during the execution of the program. Identifiers must be unique.
Example :
int marks;
float percentage;Here, marks and percentage are identifiers.
Also remember, identifier names must be different from keywords. You cannot use int and float as an identifier because int and float are keywords.
Rules for naming identifiers
- A identifier can only have letters (both uppercase and lowercase letters), digits and underscores.
- The first character of an identifier can only contain a letter (both uppercase and lowercase) or an underscore(_).
- We cannot use keywords like
float,for,whileetc. as identifiers. - Indentifiers are case-sensitive in C. Example - name and Name are two different identifiers in C.
- We cannot use special characters like semicolon, period, whitespaces, comma in or as identifiers except underscore (_).
Note : Always use meaningful names for identifiers that make sense to easily understand and modify.
Next Tutorial
We hope that this tutorial helped you develop better understanding of the concept of Keywords & Identifiers in C.
Keep Learning : )
In the next tutorial, you'll learn about C Variables & Literals.