C Variable and Datatype

Variables And Datatypes In C Language

Variables

Variables is use to carry the value.and it can be reused many times in a program. variables used to specify the particular memory location. Variable name is user defined name variable defined once will remain same . During program execution value of variable can be changed by using operators.

1.Rules /Naming of a Variable

They must begin with a letter. It can't start with a digit.
Keyword and reserved are not allowed as variable name.
White space are not allowed in variable name.
Name of variable maximum length of 31 character.more than 31 character length are invalid.
Uppercase & lowercase letter are different in c, so variable defined with upper letter are different from lower case letter variables.
Special characters like #, $ are not allowed.
Variable names are case sensitive.

2.Syntax/ Define a Variable

datatype variable-name;

3.Declaration of a Variable

int x;
char y;
float z;

4.Initialization of Variable
int x=10;
char a='xyz';
float f=34.12;

5.Types of Variable in C

1.Local Variable: A variable that defined within a the function is called local variable.
Example:
void add()
{
int a=20;//local variable
}

2.Global Variable: A Variable that defined outside the function is called global variable.
Example:
int a=20;//global variable
void add()
{
int b=10;//local variable
}

3.Static Variable: Static variable can be defined inside or outside the function. A variable declared with a static keyword is called static variable.

Example:
void add()
{
int a=10;//local variable
static int b=20;//static variable
a=a+1;
b=b+1;
printf("%d,%d",a,b);
}

4.External variable: A variable declared outside the function is called external variable. A variable is declared with extern keyword
is called external variable.
Example:
extern int a=20;//global variable
void add()
{
int b=10;//local variable
}

5.Automatic variable:A variable declared within the function is called automatic variable. A variable is declared with auto keyword is called automatic variable.

Example:

void add(){

int a=10;//local variable(also automatic)

auto int b=20;//automatic variable

}

Datatypes in C language

Datatype defines the type of the variable here type of the variable means its may be integer,float,character,boolean etc.
According the datatype program assign memory to the variable for example if a datatype is a integer of a variable then 4 bit memory assign to that variable.

C datatype are used to