---

Identifier

It is a Name which is use to identify different type of programing elements such as Variables , Constants ,Functions….etc

Rule for defining identifier

• An identifier must start with alphabets [a to z] [A to Z] or underscore [ _ ].
• Next letters of an identifier can be alphabets [a to z] [A to Z], underscore [ _ ] or digits [0 to 9] .
• Language keywords are no allowed as identifier.
• Max length of identifier can be 31 letters but it can vary depending on different compilers.
• No special symbols [eg. #,$..etc] are allowed. Except [_]

---

Keywords

• Keywords are those words whose meaning is already defined by Compiler.
• C Keywords are also called as Reserved words.
• There are 32 Keywords in C.

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

---

TOKENS

• Tokens are the basic buildings blocks in C language which are used together to write a C program.
• Each and every smallest individual units in a C program are known as Token.
• C tokens are of six types.
They are,
• Keywords               (eg: int , if , else )
• Identifiers              (eg: main , num , printf )
• Constants              (eg: 10 , 2 , 0 )
• Strings                    (eg: "Even" , "Odd" )
• Special symbols   (eg: ( ) , { } , ; )
• Operators              (eg: % , = , == )

---

Constants Literals

• These are fixed values in our program that do not change during its execution.
• These fixed values are also called literals. 
• Constants can be of any of the basic data types like an
1. integer constant
2. floating constant
3. character constant
4. string literal

---

Integer Constants

• Integer constants are whole numbers without any fractional part or exponential part.
• It can either be positive or negative, If no sign precedes it is assumed to be positive by default.
• An integer constant can be a decimal, octal, or hexadecimal.
for ex:
• Decimal :   4117 , - 6362 etc.    No prefix required
• Hexadecimal :   0x31AF , 0x123C etc.    Prefix 0x is required
• Octal :   0412 , 0667 etc .    Prefix 0 is required

---

Real /Floating Point Constants

• A floating point constant has a integer part, a decimal point, a fractional part and may contain an exponential part.
• Floating point literal may be positive or negative but must have a decimal point.
• It can be in fixed and scientific notation.

for ex:

• Fixed : 1234.5432 , -100.001 etc.
• Scientific : 2.37E-3 , 2.37e-3 [2.37 x 10^-3] etc.

---

Character Constants

• Characters constants are enclosed in a single quotes.
• They contains only single char value in it.
for ex:

• 'a', 'A', '1', '#' , '\n' are character constants

---

String constants

• String constants are enclose in double quotes.
• It may contain one or more chars in it.
For eg:
• "Amravati"
• "123"
• "3.14"
• A""

---

Modified Datatypes

These modified data types are created using a modifier short , long , unsigned , signed etc.

• unsigned int
• Memory size 2 / 4 bytes
• Range 0 to 65,535 (2^16 )
• Range 0 to 4,294,967,295 ( 2^32 )
• unsigned long int
• Memory size 4 bytes
• Range 0 to 4,294,967,295 ( 2^32 )
• unsigned short int
• Memory size 2 bytes
• Range 0 to 65,535 ( 2^16 )
• long int
• Memory size 4 bytes
• Range -2,147,483,648 to 2,147,483,647 ( ±2^31 )
• short int
• Memory size 2 bytes
• Range -32,768 to 32,767 ( ±2^15 )
• long double
• Memory size 10 bytes
• Range 3.4E-4932 to 1.1E+4932

---