Storage Classes.pdf DJJKLF DKFF DSLKF. DSF; FD

Storage Class of Variables
• It refers to the permanence of a variable, and its
scope within a program.
• Four storage class specifications in C
• Automatic: auto
• External: extern
• Static: static
• Register: register

Automatic Variables
• These are always declared within a function and are
local to the function in which they are declared.
• Scope is confined to that function.
• This is the default storage class specification.
• All variables are considered as auto unless explicitly
specified otherwise.
• The keyword auto is optional.
• An automatic variable does not retain its value once control
is transferred out of its defining function.

Example: Auto
#include <stdio.h>
int factorial(int m)
{
auto int i;
auto int temp = 1;
for (i=1; i<=m; i++)
temp = temp * i;
return (temp);
}
void main()
{
auto int n;
for (n=1; n<=10; n++)
printf (“%d! = %d n”,n, factorial (n));
}

Static Variables
• Static variables are defined within individual functions and
have the same scope as automatic variables.
• Unlike automatic variables, static variables retain their
values throughout the life of the program.
• If a function is exited and re-entered at a later time, the static
variables defined within that function will retain their previous
values.
• Initial values can be included in the static variable declaration.
• Will be initialized only once.
• An example of using static variable:
• Count number of times a function is called.

Example: Static
#include <stdio.h>
void print()
{
int count = 0;
printf("Hello World!! ");
count++;
printf("is printing %d times.n",count);
}
int main()
{
int i = 0;
while(i<10)
{
print();
i++;
}
return 0;
}
Output
Hello World!! is printing 1 times.

Example: Static
#include <stdio.h>
void print()
{
static int count = 0;
count++;
}
int main()
{
int i=0;
while(i<10)
{
print();
i++;
}
return 0;
}
Output!

External Variables
• They are not confined to single functions.
• Declare them outside the function, at the
beginning.
• Their scope extends from the point of definition
through the remainder of the program.
• They may span more than one functions.
• Also called global variables.
• Alternate way of declaring global variables.

Example: Global
#include <stdio.h>
extern int count = 0;
void print()
{
count++;
}
int main()
{
int i=0;
while(i<10)
{
print();
i++;
}
return 0;
}
Output!

Static versus Extern
#include <stdio.h>
void print()
{
static int count=0;
count++;
printf("is printing %d
times.n",count);
}
int main()
{
int i=0;
while(i<10)
{
print();
i++;
}
return 0;
}
#include <stdio.h>
extern int count=0;
void print()
{
count++;
}
int main()
{
int i=0;
while(i<10)
{
print();
i++;
printf("is printing %d
times.n",count);
}
return 0;
}

Register Variables
• These variables are stored in high-speed registers within the
CPU.
• Commonly used variables like loop variables/counters may be
declared as register variables.
• Results in increase in execution speed.
• User can suggest, but the allocation is done by the compiler.

Example Register Variables
#include<stdio.h>
int main()
{
int sum;
register int count;
for(count=0;count<20;count++)
sum=sum+count;
printf("nSum of Numbers:%d", sum);
return(0);
}

Storage Classes.pdf DJJKLF DKFF DSLKF. DSF; FD

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