Declaration of variables in c:
Declaration of
variables means to acknowledge the compiler only about variable name and its
data type with its modifiers but compiler doesn’t reserve any memory for the
variables.
In c we can
declared any variable with help of extern keyword while it has not initialized. Example of declaration:
(1) extern int a;
(2)extern struct student{
char * name;
int roll;
double marks;
};
Important points about declaration variables in c:
(1) Since
declaration variable doesn’t get any memory space so we cannot assign any value
to variable. For example:
#include<stdio.h>
extern int a;
int main(){
a=100;
printf("%d",a);
return 0;
}
Output:
Compilation error
(2) We cannot
use any operator with a variable which has only declared.
(3)We can
declare any variable either globally or locally.
(4)A same
variable can be declared many times.
Definition of
variables in c:
A c statement in which a
variable gets a memory is known as definition of variable. All auto, register,
static and initialized extern variable are example of definition of variables.
For example:
(a)
int a; //Definition of variable a
static int a; //Definition of variable a
register int a; //Definition of variable a
extern int a=5; //Definition of variable a
Note: In the
above c statement all variables has been declared and defined at the same time.
(b)
#include<stdio.h>
extern int a; //Declaration of variable a
extern int a; //Again declaration of variable a
int a=5; //Definition of variable a
int main(){
ptintf("%d",a);
return 0;
}
Output: 5
Important points
about definition of variable:
(1)If any variable has not
declared then it declaration occurs at the time of definition.
(2)We can use any operator
after the definition of variable.
(3)Definition of variables
can be globally or locally.
(4)A register variable gets
CPU instead of memory in definition.
(5)A static or extern
variable gets memory at the compile time while auto and register variables get
memory or CPU at the run time.
1 comment:
Great :)
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