VMS Help CC, Language topics, Statements, for  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The for statement executes a statement zero or more times, with
  three specified control expressions.  Expression-1 is evaluated
  only once, before the first iteration; expression-2 is evaluated
  before every iteration; expression-3 is evaluated after every
  iteration.  The for loop terminates if, on evaluation, expression-2
  is 0.
  Syntax:

       for ( [expression-1] ; [expression-2] ; [expression-3] )
           statement

  The for statement is equivalent to the following format:

       expression-1;
       while ( expression-2 ) { statement expression-3; }

  You can omit any of the three expressions.  If expression-2 is
  omitted, the while condition is true.