Declaring a variable means describing its type to the compiler but not allocating any space for it. Defining a variable means declaring it and also allocating space to hold the variable. You can also initialize a variable at the time it is defined.

(a) export variable

A class field is the same for all instances of the class. An instance field is specific to an individual instance.
Instance is variable, class is an object.
if you declare one instance in a class that instance should be sharing within that class only.
if you declare one class object it will share anywhere in the current program.

Generic Variable:
Create Object Ex:-Ole-Automation . No need refer the object library.
Specific Variable:
Binding Procedure Early and Late Binding ( Can be Remove from the Memory).

The basic types of variable in C are namely char, int, double and float. First the variables have to be declared. This is done as follows:

First any of the data type defined above must be mentioned and this is followed by the name of the variable. For instance if wants to declare a variable v1 of type char it is done as follows

char v1;

While declaring a variable what happens is the data type is described to the compiler and no space or memory allocation takes place. In other words just the data types are mentioned without any memory storage for the data types. While defining the variable the declaring the data type of the variable along with space allocation for the variable takes place.

Variable is a memory location through which the actual values are stored/retrieved. Its value can be changed.

Local variables lifetime ends when the Procedure ends. Global variables lifetime begins at the start of the
script and ends at the end of the script and it can be used by any procedure within the script. Declaring a
variable by using the keyword PRIVATE makes the variable global within the script, but if declared using PUBLIC, then all scripts can refer the variable.