Scope Rules
A
region of the program where a defined variables can have its existence and
beyond that variable it cannot be accessed is known as the Scope. In C
programming there are 3 places where variables can be declared:-
·
Inside a block
or a function which is called as local
variables.
·
Outside of all
functions which is known as global variables.
·
In the
definition of function parameters which are called formal parameters.
Let us know more
about local variables, global variables and formal parameters.
Local Variables
Variables that are declared inside a block or a
function are known as ‘Local variables’. They can only be used by the
statements that are inside that block or function of code. Local variables are
not known to functions outside their own block. Here is an example of how a
local variable is used. All the variables a, b, and c are local to main()
function.
#include <stdio.h>
int main () {
/*
local variable declaration */
int a, b;
int c;
/*
actual initialization */
a = 10;
b = 20;
c = a + b;
printf ("value of a = %d, b = %d and c = %d\n", a, b, c);
return 0;
}
Global
Variables
Global variables are defined usually on the top of
the program, outside a function. Global variables hold their values throughout
the program and can be accessed inside any of the functions defined for the
program.
Any function can access a global variable. A global
variable is available for use throughout the program after its declaration.
Below we have given an example to show how a global variables are used in a
program:-
#include <stdio.h>
/*
global variable declaration */
int g;
int main () {
/*
local variable declaration */
int a, b;
/*
actual initialization */
a = 10;
b = 20;
g = a + b;
printf ("value of a = %d, b = %d and g = %d\n", a, b, g);
return 0;
}
A program can have same name for global and local variables
but the value of local variable inside a function will take preference. Here is
an example −
#include <stdio.h>
/*
global variable declaration */
int g = 20;
int main () {
/*
local variable declaration */
int g = 10;
printf ("value of g = %d\n", g);
return 0;
}
When the above code is compiled and executed, it
gives the following result −
value
of g = 10
Formal Parameters
These are
treated as local variables within a function. They take precedence over global
variables. Following is an example:-
#include <stdio.h>
/* global variable
declaration */
int a
= 20;
int
main () {
/* local variable declaration
in main function */
int a
= 10;
int b
= 20;
int c
= 0;
printf ("value
of a in main() = %d\n", a);
c =
sum( a, b);
printf ("value
of c in main() = %d\n", c);
return 0;
}
/* function to add two
integers */
int
sum(int a, int b) {
printf ("value
of a in sum() = %d\n", a);
printf ("value
of b in sum() = %d\n", b);
return a
+ b;
}
When the above code is compiled and executed, it
gives the following result −
value
of a in main() = 10
value
of a in sum() = 10
value
of b in sum() = 20
value
of c in main() = 30
Initializing Local and Global
Variables
When we define a local variable, we must initialize
it our self as it is not initialized by the system. Global variable are
automatically initialized by the system when we define them as follows:-
|
Data Type
|
Initial Default Value
|
|
int
|
0
|
|
char
|
'\0'
|
|
float
|
0
|
|
double
|
0
|
|
pointer
|
NULL
|
It is a good programming practice to initialize
variables properly, otherwise our program may produce unexpected results, as
uninitialized variables will take some garbage value already available at their
memory location.
No comments:
Post a Comment