C Tokens
•
•
•
•
•
Identifiers
Keywords
Constants
Operators
Special symbols
Identifiers
• Identifiers are names given to various program
elements such as variables, functions and
arrays etc,.
• Eg: #define N 10
#define a 15
Here N and a are user defined identifiers.
Rules for naming identifier
• First character must be alphabetic or underscore.
• Must consist only of alphabetic characters, digits, or
underscores.
• Only the first 31 characters of an identifier are
significant and are recognized by the compiler.
• Cannot use a keywords or reserved word (e.g. main,
include, printf & scanf etc.).
• No space are allowed between the identifiers etc,.
• C is case sensitive, e.g. My_name  my_name.
Examples of Valid and Invalid Names
Valid Names
Invalid Names
a
a1
$sum
/* $ is illegal */
student_name
stdntNm
2names
/* Starts with 2 */
_aSystemName
_anthrSysNm stdnt Nmbr /* no spaces */
TRUE
FALSE
int
/* reserved word */
Variables
• Variable is an identifier that is used to
represent some specified type of information.
• Eg: x=3
• Here x is variable.
Keywords
• It is a reserved words.
• Cannot be used for anything else.
• Examples:
– int
– while
– for etc,.
Keywords
Auto
Double
Int
Struct
Break
Else
Long
Switch
Case
Enum
Static
register
typedef
Char
extern
return
union
Const
Float
short
unsigned
While
Continue
For
signed
void
Default
Goto
sizeof
do
If
Constants
• It is an entity whose value does not changes
during the execution.
• Eg: x=3
• Here 3 is a constant.
Types
• Numeric constants
• Character constant
Constants
Constants
Numeric Constants
Integer
Constant
Real
Constant
Character Constants
Single
Character
Constant
String
Constant
Numeric constants
Integer constants
• It is formed using a sequence of digits.
Decimal - 0 to 9 .
Octal
- 0 to 7.
Hexa
- 0 to 9 ,A to F
Eg: 10,75 etc.
Rules for defining Integer Constant
•
•
•
•
It must have atleast one digit.
Decimal point are not allowed.
No blank space or commas are allowed.
It can be either positive or negative. Etc,.
Numeric constants
Real constants
• It is formed using a sequence of digits but it
contain decimal point.
• length, height, price distance measured in real
number
Eg: 2.5, 5.11, etc.
Character constants
Single character constant
– A character constant is a single character they also
represented with single digit or a single special
symbol which is enclosed in single quotes.
– Eg: ‘a’, ‘8’,’_’etc.
Character constants
String constants
• String constant are sequence of characters enclosed
with in double quote.
• Eg: “Hello” ,”444”,”a” etc,.
Operators
• An operator is a symbol that specifies an
operation to be performed on the operands.
• Eg: a + b
+ is an operator.
a,b are operands.
Data Types
 A Data type is the type of data that are
going to access within the program.
Standard Data Types
These Standard type can be used to build
more complex data types called Derived
Types (e.g. pointers, array, union etc.).
Data types
Data type Size(bytes)
Range
Format string
Char
1
-128 to 127
%c
int
2
-32,768 to 32,767
%d
Float
4
3.4 e-38 to 3.4 e+38
%f
Double
8
1.7 e-308 to 1.7 e+308
%lf
integer


A number without a fraction part : integral
number.
C supports three different sizes of the integer
data type :
 short int
 int
 long int
Floating Point
A floating-point type is a number with a
fractional part, e.g. 56.78
 Floating point numbers are stored using
4 Byte.
 Types




Float
Double
long double
character
• Character are generally stored using 8 bits(1
Byte) of the internal storage.
Character
ASCII code value
a
97(decimal) or 01100001(binary)
x
120(decimal) or 01111000(binary)
void


The void type has no values and no operations.
Both the set of values and the set of operations
are empty.
Variable’s Declaration

To create a variable, you must specify the
type and then its identifier :
float price;
int a,b;
char code;
Entire Data types in c:
Data type
Size(bytes)
Range
Format string
Char
1
128 to 127
%c
Unsigned char
1
0 to 255
%c
Short or int
2
-32,768 to 32,767
Unsigned int
2
0 to 65535
Long
4
Unsigned long
4
0 to 4294967295
Float
4
3.4 e-38 to 3.4 e+38
Double
8
1.7 e-308 to 1.7 e+308
%lf
Long Double
10
3.4 e-4932 to 1.1 e+4932
%lf
-2147483648 to 2147483647
%i or %d
%u
%ld
%lu
%f or %g