/sys$common/syshlp/helplib.hlb CC, Language topics, Statements, do  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The do statement executes a statement one or more times, as long as
  a stated condition expression is true.
  Syntax:

       do statement while ( expression ) ;

  The do statement is executed at least once.  The expression is
  evaluated after each execution of the statement.  If the expression
  is not 0, the statement is executed again.  The statement following
  the do statement (the body of the do statement) is not optional;
  the null statement (a lone semicolon) is provided for specifying a
  do statement with an empty body.