1. C Tokens
Identifiers
Keywords
Constants
Operators
Special symbols

2. 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.

3. 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.

4. Examples of Valid and Invalid Names

5. Variables
Variable is an identifier that is used to represent some specified type of information.
Eg: x=3
Here x is variable.

6. Keywords It is a reserved words. Cannot be used for anything else.
Examples:
int
while
for etc,.

7. Keywords Auto register Continue Double typedef For Int Char signed
Struct extern void
Break return Default
Else union Goto
Long Const sizeof
Switch Float do
Case short If
Enum unsigned
Static While

8. Constants
It is an entity whose value does not changes during the execution.
Eg: x=3
Here 3 is a constant.

9. Types
Numeric constants
Character constant

10. Constants Constants Integer Constant Real Constant Single Character
Numeric Constants
Character Constants
Integer
Constant
Real
Constant
Single
Character
Constant
String
Constant

11. 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.

12. 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,.

13. 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.

14. Character constants Eg: ‘a’, ‘8’,’_’etc. 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.

15. Character constants String constants
String constant are sequence of characters enclosed with in double quote.
Eg: “Hello” ,”444”,”a” etc,.

16. 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.

17. Data Types
A Data type is the type of data that are going to access within the program.

18. Standard Data Types
These Standard type can be used to build more complex data types called Derived Types (e.g. pointers, array, union etc.).

19. Data types Data type Size(bytes) Range Format string
Char to %c
int ,768 to 32, %d
Float e-38 to 3.4 e %f
Double e-308 to 1.7 e %lf

20. integer A number without a fraction part : integral number.
C supports three different sizes of the integer data type :
short int
int
long int

21. Floating Point
A floating-point type is a number with a fractional part, e.g
Floating point numbers are stored using
4 Byte.
Types
Float
Double
long double

22. character
Character are generally stored using 8 bits(1 Byte) of the internal storage.
Character ASCII code value
a (decimal) or (binary)
x (decimal) or (binary)

23. void The void type has no values and no operations.
Both the set of values and the set of operations are empty.

24. Variable’s Declaration
To create a variable, you must specify the type and then its identifier :
float price;
int a,b;
char code;

25. Entire Data types in c: Data type Size(bytes) Range Format string
Char to %c
Unsigned char to %c
Short or int ,768 to 32, %i or %d
Unsigned int to %u
Long to %ld
Unsigned long to %lu
Float e-38 to 3.4 e %f or %g
Double e-308 to 1.7 e %lf
Long Double e-4932 to 1.1 e %lf