1. C
Storage classes

2. Storage classes in C
Storage Classes are used to describe about the features of a variable/function. These features basically include the scope, default initial values and life- time which help us to trace the existence of a particular variable during the runtime of a program. Storage classes also tells the compiler where to store a variable, how to store the variable, what is the initial value of the variable and life time of the variable.

3. Storage classes in C
Scope: i.e. where the value of the variable would be available inside a program.
Default initial value: i.e. if we do not explicitly initialize that variable, what will be its default initial value.
Lifetime of that variable: i.e. for how long will that variable exist.
Storing values: All variables defined in a C program get some physical location in memory where variable's value is stored. Memory and CPU registers are types of memory locations where a variable's value can be stored.

4. Storage classes in C Automatic variables External variables
Static variables
Register variables
The general form of a variable declaration that uses a storage class is shown here:
storage_class_specifier data_type variable_name;

5. Storage classes in C (Automatic variables)
Automatic variables can also be called local variables because they are local to a function. By default they are assigned garbage value by the compiler.
Storage place: CPU Memory
Initial/default value: Garbage value
Scope: local
Life: Within the function only.

6. Storage classes in C (Automatic variables)
#include <stdio.h>
int main( ) {
auto int i = 1;
auto int i = 2;
auto int i = 3;
printf ( "\n%d ", i); }
printf ( "%d ", i);
printf( "%d\n", i);
#include<stdio.h>
void main() {
int detail;
// or
auto int details; //Both are same }

7. Storage classes in C (External variables)
The principal use of extern is to specify that a variable is declared with external linkage elsewhere in the program.
Means we can declare variable and define at any place.
Storage place: CPU memory
Initial/default value: Zero
Scope: Global
Life: Till the end of the main program. Variable definition might be anywhere in the C program.

8. Storage classes in C (External variables)
int main() { extern int x; //informs the compiler that it is defined somewhere else printf("%d", x); } int x=2; //Global variable x Also, if you change the statement extern int x; to extern int x = 50; you will again get an error "Redefinition of 'x'" because with extern specifier the variable cannot be initialized, if it is defined elsewhere.

9. Storage classes in C (Static variables)
A static variable tells the compiler to persist/save the variable until the end of program.
Storage place: CPU memory
Initial/default value: Zero
Scope: local
Life: Retains the value of the variable between different function calls.

10. Storage classes in C (Static variables)
void test() {
static int a = 0; //a static variable
a = a + 1;
printf("%d\t",a); }
#include<stdio.h>
void test(); //Function declaration (discussed in next topic)
int main() {
test(); }

11. Storage classes in C (register variables)
The register storage class is used to define local variables that should be stored in a register instead of RAM. This means that the variable has a maximum size equal to the register size. Can't have the unary '&' operator applied to it (as it does not have a memory location). Use: A register declaration is equivalent to an auto declaration, but hints that the declared variable will be accessed frequently; therefore they are placed in CPU registers, not in memory. Only a few variables are actually placed into registers

12. Storage classes in C (register variables)
int main() {
register int i = 10;
// int i=10;
printf("Value of i: %d", i);
printf("\n Address of i: %u", &i); }
Value of i: 10
Address of i:
Storage place: Register memory
Initial/default value: Garbage value
Scope: local
Life: Within the function only.

13. Assignment
Write sample C program to check variability scope of auto storage class.
Write simple C program to find factorial of given range number using static storage class concept
1 fact is 1
2 fact is 2
3 fact is 6
Write any c program to find use of external storage class
Write any c program to show drawbacks of register storage class

15. #include<stdio.h>
void test(); //Function declaration (discussed in next topic)
int main() {
int i;
for (i=1;i<=5;i++){
test(i); }
void test(int aa)
static int a = 1; //a static variable
a = a *aa;
printf("%d fact is %d\n",aa, a);