Part-2 Variable and
Data type
Variable:
A variable in program is specific
piece of memory. Every variable in a program has a name. We use variable to
store a data value in memory and retrieve the data that is stored in it.
Rules for giving a Name to variable:- (wrong declaration highlighted by red color)
a) A variable name only contains characters, digits and underscore.
Variable names like oh! , Mike-Jack not allowed.
b) The first letter of variable name must be letter or
underscore. Variable name must not be started with a digit like 8_oclock, 6_pack. Never
try to start variable name with underscore because variable name started with
underscore already declared in libraries which can cause quite confusion to
understand.
c) No comma or blank space is provided within variable name.
d) Variable names are case-sensitive. If you declare length
and Length are distinct.
e) Always try to give Variable name as short as possible and
maximum of 31 characters. Giving large name will increase your typing effort.
f) You cannot provide C’s Keyword like main, switch as
Variable name.
Data Type:
Data type can be defined as type of
data of variable. Whenever we declare a variable, we have to mention what kind
of data it can hold or store. C offers Standard and minimal set of data type.
Sometimes called as “Primitive Data Type”.
For example:-
int num; //here
int is Data Type
char name; //here
char is Data Type
C language Data type can be classified into 3 type:-
1) Primary Data Type 2) Derived Data Type (e.g. Array,
Pointer, Structure, Union) 3) User defined Data Type
Primary Data Type divided into four basic data types:-
|
|
|
|
|
|
Data
Type
|
Description
|
Size(in byte)
|
Range
|
|
char
|
Character
|
1
|
-128 to +127
|
|
int
|
Integer
|
2
or 4
|
-32768
to +32767
|
|
float
|
Number with
decimal point. Precision upto 6 digits
|
4
|
-3.4e38
to +3.4e38
|
|
Double
|
Number
with decimal point. Precision upto 12 digits
|
8
|
-1.7e308
to +1.7e308
|
Size and
Range of Data Type may vary according to the qualifiers. Data Type Qualifier
can be divided into two part:-
1) Size Qualifier
2) Sign
Qualifier
Size Qualifier: Size Qualifier alter the size of data
type. There are 2 types of size qualifiers: short and long.
For Example:
Storage
space or size of int data type is 4 byte for 32 bit processor. We can increase
the range using long int whose size is 8 byte or decrease the size using short
int whose size is 2 byte.
Sign Qualifier: Signed and unsigned keyword used to
specify whether variable can store +ve number or +ve as well as –ve number.
Example:-
unsigned int range is -32768 to +32767 whereas signed int range is 0 to 65,535
Example 2.1: Finding Size of Data Type using sizeof operator
#include <stdio.h>
#include <conio.h>
void main()
{
printf("Size
of char %d byte\n",sizeof(char));
printf("Size
of int %d byte\n",sizeof(int));
printf("Size
of float %d byte\n",sizeof(float));
printf("Size
of double %d byte\n",sizeof(double));
getch();
}
On My system I get the following result
Constants:-
A Constant
is used just like a variable, though its value never changes. For example:
Value of π (pie) in trigonometry is fixed (constant) which is equal to
3.14159265.
We can
declare constant in our program in two ways:-
1) Using #define 2) Using const keyword
Using
#define:
#include <stdio.h>
#include <conio.h>
#define PI 3.14159f //defining name and
value for PI
void main()
{
float radius=2.2; //radius
float circum=2*PI*radius; //variable storing
circumference
printf("Circumference
of Circle=%f metre",circum); /*print the result on console or terminal*/
getch();
}
Using
const keyword:
#include <stdio.h>
#include <conio.h>
void main()
{
const float PI=3.14159f; //declare
PI using const
float radius=2.2; //radius
float circum=2*PI*radius; //variable
storing circumference
printf("Circumference
of Circle=%f metre",circum); /*print the result on console or terminal*/
getch();
}
When
we use const keyword,
we can specify a Data type for our constant where as in previous example (using
# define), PI was just a sequence of characters that replace all the value of
PI in your program.
