Functions consist of one or more blocks of statements that perform
  one logical operation.  They can be called from other functions
  either in the same program or in different programs.  A function
  may exchange values with the calling function by use of parameters.

  Function declarations have the following syntax:

       function_name()
  or
       function_name(arg1, arg2,...)
  or
       function_name(data-type arg1, data-type arg2,...)

  In the first form of the function declaration, the function takes
  no arguments.  In the second form, the function takes arguments;
  the arguments are declared outside the parameter list.  In the
  third form, the function declaration is a function prototype that
  specifies the type of its arguments in the identifier list; the
  prototype form is recommended.  In all three cases, the parenthesis
  after the function name are required.

  HP C for OpenVMS Systems provides a library of common functions.
  These functions perform standard I/O operations, character and
  string handling, mathematical operations, miscellaneous system
  services, and UNIX* system emulation.  For more information, see
  HELP CRTL.

 ----------
 * UNIX is a trademark of The Open Group.