DO                       Begin Definition of DO/LOOP Loop

 DO [{WHILE | UNTIL} expression]
 .
 . [statements]
 .
 [EXIT LOOP]
 [LOOP | WEND] [{WHILE | UNTIL} expression]

    Begins the definition of a DO/LOOP loop.

  expression    A numeric expression. Nonzero values are equivalent to
                TRUE, while zero values are equivalent to FALSE.

       WHILE    Causes execution of the loop as long as expression is
                TRUE.

       UNTIL    Causes execution of the loop as long as expression is
                FALSE.

   EXIT LOOP    An optional means to escape from the loop before its
                LOOP | WEND termination.

 LOOP | WEND    Terminates the loop construct. LOOP and WEND are synonyms
                in this context, but one or the other must be provided to
                match each DO statement.

   --------------------------------------------------------------------------

      Notes:    DO...LOOP is a general-purpose looping construct. The
                termination test may be supplied at the beginning, at the
                end, at both places, or at neither.