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B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.STORAGE CLASSES
The variables declared in C programs are totally different from other languages. We can use same variable names in the C program in separate blocks.
The area or block of the C program from where the variable can be accessed is known as the scope of the variable. The area or scope of the variable depends on its storage class i.e., where and how it is declared. There are four scope variables.
Function
File
Block
Function prototype.
The storage class of a variable tells to the compiler
The storage area of the variable.
The initial value of the variable if not initialized.
The scope of the variable.
Life of the variable i.e., how long the variable would be active in the program.
Any variable declared in c can have any one of the four storage classes.
Automatic variables.
External variables.
Static variables.
Register variables.
Automatic variables (auto):
Auto variables are defined inside a function. A variable declared inside the function without storage class name, by default is an auto variable. These functions are declared on the stack. The keyword auto can be used to declare the auto variables.
Example: auto int a;
For an auto variable,
The storage location is stack.
The default value is a garbage value.
The scope of the variable is local to block in which they are defined.
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B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA. The following program illustrates the working of auto variables in C.Aim: C-Program to illustrates the working of auto variables in C.
Program:
#include<stdio.h>
#include<conio.h>
void main()
{
int x=10;
clrscr();
printf("\nX=%d",x);
{
int x=20;
printf("\nX=%d",x);
}
printf("\nX=%d",x);
getch();
}
Output:
External Variables
The variables that are available to all the functions in the program i.e., from entire program they can be accessed are called an external variable or a global variable. External variables are declared outside of the function body. The keyboard extern can be used to declare an external variable.
Example: extern int a;
For an external variable,
The storage location is stack.
The default value is zero (0).
The scope of the variable is entire the program.
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B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA. The following program illustrates the working of an external storage class.Aim: To illustrates the working of an external variable in c.
Program:
#include<stdio.h> #include<conio.h> int x=10;
void main() {
clrscr(); f1(); f2();
printf("\n In main() x=%d",x); getch();
} f1() {
int x=20;
printf("\n In f1() x=%d",x); }
f2() {
printf("\n In f2() x=%d",x); }
Output:
Static Variables
If a variable is defined with the keyword static then it is called static storage class
variable. The initial value of static storage class variable is zero. We can have both the local
and global static variables.
The static is mainly used to maintain the previous value of the variable if the
programming is there or not. Generally static is used for counting the function how many
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B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA. The following program illustrates the working of a static variable.Aim: To write a C program that illustrates the working of a static variable in C.
Program:
#include<stdio.h> #include<conio.h> #include<process.h> void main()
{
void print(); clrscr();
for( ; ;) //Infinit loop {
print(); }
}
void print() {
static int m;//Default value is zero m++;
printf("\n m=%d",m); if(m>3)
{
getch(); exit(0); }
}
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B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA.B.Naresh Assistant Professor in B.V.R.I.C.E, Dept., of MCA. Register VariablesIf a variable is declared with the keyword register then it is called as register storage
class variable. When a variable is defined under the register then the value of the register then
the value of the variable directly stored in CPU registers. As we know the processor fastly
access the registers, so that the register storage class variables are fastly accessed compare to
normal variables.
As the CPU registers are less in number we have to take less number of register
variables only. If we define more number of register variables and if there is no availability
then register storage class variables automatically convert into auto storage class variable by
the compiler.
Float is not suitable for register class variable .Initial value is garbage, scope and life
time is within the block.
The following program illustrates the working of register storage class.
Aim: To write a C program that illustrates the use of a register variable in C.
Program:
#include<stdio.h>
#include<conio.h>
void main()
{
register int a;
clrscr();
a=10;
printf("\n a=%d",a);
getch();
}
Output:
