You can use this type of constant wherever numeric constants are
  allowed; it assumes a numeric data type according to its context.

  An octal constant has one of these forms:

    O'd[...d]'
    O"d[...d]"

    d   Is an octal (base 8) digit in the range 0 - 7.

  You can specify up to 128 bits in octal (43 octal digits)
  constants.  Leading zeros are ignored.