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Classes

A storage class defines the scope (visibility) and life-time of variables and/or functions
within a C Program. They precede the type that they modify. We have four different storage
classes in a C program:
 auto
 register
 static
 extern

The auto Storage Class
The auto storage class is the default storage class for all local variables.

{
int mount;

auto int month;
}

The example above defines two variables within the same storage class. ‘auto’ can only
be used within functions, i.e., local variables.

The register Storage Class
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 (usually one word) and can't have the unary '&' operator applied to it (as it does not have a
memory location).
The register should only be used for variables that require quick access such as counters.

{

register int miles;
}

It should also be noted that defining 'register' does not mean that the variable will be stored in a
register. It means that it MIGHT be stored in a register depending on hardware and
implementation restrictions.

The static Storage Class
The static storage class instructs the compiler to keep a local variable in existence during
the life-time of the program instead of creating and destroying it each time it comes into and goes
out of scope. Therefore, making local variables static allows them to maintain their values
between function calls.
The static modifier may also be applied to global variables. When this is done, it causes
that variable's scope to be restricted to the file in which it is declared.

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