Fundamentals of C Language

 

“C” Tokens

Individual words and punctuation marks are characters. In a “C” program the smallest individual units are known as “C” tokens. It has 6types of token‟s

1. Keywords
2. Identifiers
3. Constants
4. Variables
5. Data types
6. Type def

Keywords
Keyword is an predefined word ,Which is an already defined by the C-Develphers
Ex:int ,float,char,if etc...
C-Language contains 32 Keywords

Constants
Constant is an identifier whose value can't be changed.
Ex:int x=10;
Here 10 is a Constant
x is a Variable
int is a Datatype
These constants are classified into 2 types

1. Numerical Constants
2. Character Constants

• Numerical Constants:
Numerical Constants menans Numbers these are classified into 2 types
1. Integer Constants
2. Real Constants
Integer Constants: Integer constants means + or -(minus) values
Ex:int x=10;
     int y=-24;
Real Constants Real constants means floating values
Ex:float x=1.0;

• Character Constants
Character constants menas Characters these are classified into 2 types
1. Single character constants
2. String character constants
Single character Constants: If any character or symbol or number enclosed with single quotation
Ex:char ch='a'
     char ch='@';
     char ch='4';
String character Constants Group of character or symblos or numbers enclosed with double quotation
Ex:char ch[20]="varshini";

Variable

Variable
   Variable is an identifier whose value can be changed or which holds the data
Ex:int x=12;
          x=20;
Variable Declaration Rules:

1. Variable name must be start with alphabet or underscore or doller symbol
Ex:int age=12;
     int _age=24;
     int $age=45;

2. The max length of the variable name is upto 32 characcters
3. If variable name contains morethan one word ,The second word onwords first letter should be uppercase letter
Ex:int studentAge=12;
4. No spaces are allowed at the middle of the variable declaration
Ex:int student Age=24; (Invalid)
5. If variable value contains constant value that variable name must be uppercase
Ex: const float PI=3.14
       const int AGE=24;
6. If constant variablename contains morethan one word ,It should be separated with underscore
Ex:const int STUDENT_AGE=24;
7. All keywords are lowercase letters
8. We should not take keyword as a variable name
Ex: int if=12 (invalid) Here if is a keyword

Variable Defination Types

1. Initilization
2. Declaration
3. Assignment

Initilization:

It menas initilize the some value to the variable
Ex:int x=12; here 12 is initilize to the x

Declaration

In the Declaration no value initilize to the variable
Ex:int x;

Assignment

In the assignment assign the value to the variable or assign variable to the variable
Ex:int x;
     x=12;(value to variable)
     int y;
     y=x;(variable to variable)

Datatypes

Datatypes are used to identify the type of data or which allocates the sufficient memory space for the varables. These Datatypes are classified into following types:

1. Primitive Datatypes
2. Derived Datatypes
3. Userdefined Datatypes

Primitive Datatypes:

Primitive datatypes are used to store the single value at a time
Ex:int x=12;
    int y=12,13;(invalid) These Primitive datatypes are classified into following types

1. Integer datatype
2. Floating point datatypes
3. Character datatypes
4. Void Datatypes

Derived Datatypes:

These are used to store the morethan one value similar type
Ex:Arrays--- int marks[]={12,12,12,12,12,12}

Userdefined Datatypes:

These are used to store the morethan one value dissimilar type
Ex:structure,union

Type def : Defined as type definition by using typedef we can create new datatype. Typedef type data _ame;
Type ---- datatype
Dataname---- Name of that type