Prevents specified variables, arrays, and common blocks from being
  optimized during compilation.

  The VOLATILE attribute can be specified in a type declaration
  statement or VOLATILE statement, and takes one of the following
  forms:

  Type Declaration Statement:

   type, [att-ls,] VOLATILE [,attr-ls] :: obj [,obj]...

  Statement:

   VOLATILE obj [,obj]...

     type      Is a data type specifier.

     attr-ls   Is an optional list of attribute specifiers.

     obj       Is the name of an object or a common block
               enclosed in slashes.

  A variable or COMMON block must be declared VOLATILE if it can be
  read or written in a way that is not visible to the compiler.  For
  example:

   o  If an operating system feature is used to place a variable in
      shared memory (so that it can be accessed by other programs),
      the variable must be declared VOLATILE.

   o  If a variable is modified by a routine called by the operating
      system when an asynchronous event occurs, the variable must be
      declared VOLATILE.

  If an array is declared VOLATILE, each element in the array becomes
  volatile.  If a common block is declared VOLATILE, each variable in
  the common block becomes volatile.

  If an object of derived type is declared VOLATILE, its components
  become volatile.

  If a pointer is declared VOLATILE, the pointer itself becomes
  volatile.

  A VOLATILE statement cannot specify the following:

   o  A procedure

   o  A function result

   o  A namelist group

  The VOLATILE attribute is compatible with the ALLOCATABLE,
  AUTOMATIC, DIMENSION, INTENT, OPTIONAL, POINTER, PRIVATE, PUBLIC,
  SAVE, STATIC, and TARGET attributes.