C Programming - Variables And Constants

Variables And Constants

Variables

• Variable in C Programming is called as container to store the data.
• Variable name may have different data types to identify the type of value stored.
• Suppose we declare variable of type integer then it can store only integer values.
• Variable is considered as one of the building block of C Programming which is also called as identifier.
• A Variable is a name given to the memory location where the actual data is stored.

Following are the types of variable in C :

• Local Variables
• Global Variables

Local Variables

• Local Variable is Variable having Local Scope.
• Local Variable is accessible only from function or block in which it is declared.
• Local variable is given Higher Priority than the Global Variable.

Global Variables

• Global Variable is Variable that is Globally available.
• Scope of Global variable is throughout the program [ i.e in all functions including main() ]
• Global variable is also visible inside function , provided that it should not be re-declared with same name inside function because "High Priority is given to Local Variable than Global"
• Global variable can be accessed from any function.

Rules For Variable Name

1. Characters allowed : Underscore(_), Capital Letters ( A - Z ), Small Letters ( a - z ), and Digits ( 0 - 9 ).
2. Blank spaces and commas are not allowed.
3. No Special Symbols other than underscore(_) are allowed.
4. First Character should be alphabet or Underscore.
5. Variable name Should not be Reserved Keywords.

Keywords

Keywords are reserved words which have standard, predefined meaning in C. They cannot be used as program-defined identifiers

*Generally all keywords are in lower case although uppercase of same names can be used as identifiers.

List of C keywords are as follows :

char

int

long

union

continue

goto

while

if

double

enum

const

for

sizeof

do

else

struct

register

float

signed

volatile

typedef

switch

break

extern

short

void 

auto 

case 

static 

return

unsigned 

default

Data Types

• DataTypes are used for declaring variables And functions of different types.
• When Program store data in variables, It is necessary that each variable must be assigned a specific data type.

Following are the list of Data Types in C :

Keyword	Memory	Range
char or signed char	1 Byte	-128 to 127
unsigned char	1 Byte	0 to 255
int or signed int	2 Byte	-32,768 - 32,767
unsigned int	2 Byte	0 to 65535
short int or signed short int	1 Byte	-128 to 127
unsigned short int	1 Byte	0 to 255
long or signed long	4 Bytes	-2,147,483,648 to 2,147,483,647
unsigned long	4 Bytes	0 to 4,294,967,295
float	4 Bytes	3.4E - 38 to 3.4E + 38
double	8 Byte	1.7E - 308 to 1.7E + 308
long double	10 Bytes	3.4E-4932 to 1.1E + 4932

Declaration of variable :

main()
{
    /* declaration */

    //long int is datatype and amount is variable name
    long int amount;

    //int is datatype and code is variable name
    int code;

    char c;

    double average;

    float x,y;

}

Constants

A constant is an identifier with an associated value which cannot be altered by the program during execution.

How to declare constant variable ?

We can declare constant variable using const keyword.

Example of declaring constant variable

//Syntax for declaring constant variable
data type const variable_name = value;

//float constant
float const pi = 3.14;

//integer constant
int const a = 5;

//character constant
char const yes = 'y';

Symbolic Constant

Symbolic Constant is a name that substitutes for a sequence of a characters or a numeric constant, a character constant or a string constant.
The syntax is as follow :
#define name text
where,
name implies symbolic name in a caps
text implies value or the text.
For Example :

#define printf print
#define MAX 100
#define TRUE 1
#define FALSE 0
#define SIZE 0

The # character is used for preprocessor commands. A preprocessor is a system program, which comes into action prior to Compiler, ans it replaces the replacement text by the actual tet. This will allow correct use of the statement printf