C Programming Keywords and Identifiers
Character set
Character set are the set of alphabets, letters 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 8 9
Special Characters:
Special Characters in C language
,
<
>
.
_
(
)
;
$
:
%
[
]
#
?
'
&
{
}
"
^
!
*
/
|
-
\
~
+
White space Characters:
blank space, new line, horizontal tab, carriage return and form feed
Keywords:
Keywords are the reserved words used in programming. Each keywords has fixed meaning and that cannot be changed by user. For example:
int money;
Here, int is a keyword that indicates, 'money' is of type integer.
As, C programming is case sensitive, all keywords must be written in lowercase.
Keywords in C Language
auto
double
int
struct
break
else
long
switch
case
enum
register
typedef
char
extern
return
union
continue
for
signed
void
do
if
static
while
default
goto
sizeof
volatile
const
float
short
unsigned
Besides these keywords, there are some additional keywords supported by Turbo C.
Additional Keywords for Borland C
asm
far
interrupt
pascal
near
huge
cdecl
All these keywords, their syntax and application will be discussed in their respective topics.
Identifiers
In C programming, identifiers are names given to C entities, such as variables, functions, structures etc. Identifier are created to give unique name to C entities to identify it during the execution of program. For example:
int money;
int mango_tree;
Here, money is a identifier which denotes a variable of type integer. Similarly, mango_tree is another identifier, which
denotes another variable of type integer.
Rules for writing identifier
1. An identifier can be composed of letters (both uppercase and lowercase letters), digits and underscore '_' only.
2. The first letter of identifier should be either a letter or an underscore. But, it is discouraged to start an identifier name with an underscore though it is legal. It is because, identifier that starts with underscore can conflict with system names. In such cases, compiler will complain about it. Some system names that start with underscore are _fileno, _iob, _wfopen etc.
3. There is no rule for the length of an identifier. However, the first 31 characters of an identifier are discriminated by the compiler. So, the first 31 letters of two identifiers in a program should be different.
Tips for Good Programming Practice :
Programmer can choose the name of identifier whatever they want. However, if the programmer choose meaningful name for an
identifier, it will be easy to understand and work on, particularly in case of large program.
C Programming Variables and Constants
Variables
Variables are memory location in computer's memory to store data. To indicate the memory location, each variable should be given a unique name called identifier. Variable names are just the symbolic representation of a memory location. Examples of variable name: sum, car_no, count etc.
int num;
Here, num is a variable of integer type.
Rules for writing variable name in C
1. Variable name can be composed of letters (both uppercase and lowercase letters), digits and underscore '_' only.
2. The first letter of a variable should be either a letter or an underscore. But, it is discouraged to start variable name with an underscore though it is legal. It is because, variable name that starts with underscore can conflict with system names and
compiler may complain.
3. There is no rule for the length of length of a variable. However, the first 31 characters of a variable are discriminated by the compiler. So, the first 31 letters of two variables in a program should be different.
In C programming, you have to declare variable before using it in the program.
Constants
Constants are the terms that can't be changed during the execution of a program. For example: 1, 2.5, "Programming is easy." etc. In C, constants can be classified as:
Integer constants
Integer constants are the numeric constants(constant associated with number) without any fractional part or exponential part. There are three types of integer constants in C language: decimal constant(base 10), octal constant(base 8) and hexadecimal constant(base 16) .
Decimal digits: 0 1 2 3 4 5 6 7 8 9
Octal digits: 0 1 2 3 4 5 6 7
Hexadecimal digits: 0 1 2 3 4 5 6 7 8 9 A B C D E F.
For example:
Decimal constants: 0, -9, 22 etc
Octal constants: 021, 077, 033 etc
Hexadecimal constants: 0x7f, 0x2a, 0x521 etc
Notes:
1. You can use small caps a, b, c, d, e, f instead of uppercase letters while writing a hexadecimal constant.
2. Every octal constant starts with 0 and hexadecimal constant starts with 0x in C programming.
Floating-point constants
Floating point constants are the numeric constants that has either fractional form or exponent form. For example:
-2.0
0.0000234
-0.22E-5
Note:Here, E-5 represents 10-5. Thus, -0.22E-5 = -0.0000022.
Character constants
Character constants are the constant which use single quotation around characters. For example: 'a', 'l', 'm', 'F' etc.
Escape Sequences
Sometimes, it is necessary to use newline(enter), tab, quotation mark etc. in the program which either cannot be typed or has special meaning in C programming. In such cases, escape sequence are used. For example: \n is used for newline. The backslash( \ ) causes
"escape" from the normal way the characters are interpreted by the compiler.
Escape Sequences
Escape Sequences