A variable is a data object whose value can be changed at any point
  in a program.  It can be any of the following:

   o  A scalar name

      A scalar is a single object that has a single value; it can be
      of any intrinsic or user-defined type.

   o  An array name

      An array is a collection of scalar elements of any intrinsic or
      derived type.  All elements must be have the same type and kind
      type parameter.

   o  A subobject designator

      A subobject is part of an object.  The following are
      subobjects:

        An array element
        An array section
        A structure component
        A substring

      For example, B(3) is a subobject (array element) designator for
      array B.  A subobject cannot be a variable if its parent object
      is a constant.

  The name of a variable is associated with a single storage
  location.

  Variables are classified by data type, as constants are.  The data
  type of a variable indicates the type of data it contains,
  including its precision, and implies its storage requirements.
  When data of any type is assigned to a variable, it is converted to
  the data type of the variable (if necessary).

  A variable is usually defined in a type declaration statement or
  DATA statement.  But during program execution, events can occur to
  cause variables to be defined or redefined (such as assignment
  statements and READ statements), or undefined (such as an I/O
  error).

  Scalar variables are assigned data types explicitly in type
  declaration statements or IMPLICIT statements, or they can have
  implicit data types.