INDEX (string, substring [,back] [,kind])

  Class:  Elemental function - Generic

  Returns the starting position of the substring as an INTEGER*4 or
  INTEGER*8 value.

  "string" and "substring" are of type character, "back" is of type
  logical, and "kind" is a scalar integer initialization expression.

  The result is of type integer.  If "kind" is present, the kind
  parameter of the result is that specified by "kind"; otherwise, the
  kind parameter of the result is that of default integer.  If the
  processor cannot represent the result value in the kind of the
  result, the result is undefined.

  Examples:

  INDEX ('FORTRAN', 'O', BACK = .TRUE.) has the value 2.

  INDEX ('XXXX', " ", BACK = .TRUE.) has the value 0.

  INDEX ('XXXX', "", BACK = .TRUE.) has the value 5.