7.2.2.1 Declarative DIM Statements
  Declarative DIM statements have integer constants as
  bounds. The percent sign is optional for bounds; however,
  BASIC signals the error ``Integer constant required'' if a
  constant bound contains a decimal point. The following state-
  ment creates a 101-element virtual array containing string
  data. The elements of this array can each have a maximum
  length of 256 characters.
  DIM #1%, STRING VIRT_ARRAY(100) = 256%

  The following restrictions apply to the use of declarative DIM
  statements:

  .
        A declarative DIM statement must lexically precede any
        reference to the array it dimensions.
  .
        The lower bounds of all virtual array dimensions must be
        zero.
  .
        You must open a VIRTUAL file on the specified channel
        before you can access elements of the virtual array.