implml.f

C  Author:   Mitch Richling<http://www.mitchr.me/>
C  IP:       Copyright 1993 by Mitch Richling.  All rights reserved.
C  Key word: FORTRAN f77 do
C  Notes:    Illustrates the IMPLICIT NONE extension to FORTRAN 77 that
C            was specified by MIL-STD-1753 (A Department of Defense
C            standard issued in 1988).  The extensions were REQUIRED for
C            a complier to be used for a DoD project, and today they are
C            required for most government contract work with FORTRAN 77.
C            This extension was already supported by many compilers before
C            MIL-STD-1753, and it is supported by almost all modern
C            FORTRAN 77 compilers.  
C
C            This statement is part of the Fortran 90 standard.
C
C            Note that many compilers have
C            a compile time option that will provide warnings for
C            implicit variable declarations regardless of the
C            use of IMPLICIT NONE (with g77 use -Wimplicit)

C             IMPLicit MiL standard
      program implml

C     Making implicit variables illegal is as simple as placing
C     the following before any executable code in every unit
C     unit (main program, subroutine, function, etc...)
      implicit none

C     Declare and use a variable i.
      integer i

C     If uncommented, the following line would be illegal:
C      j = 1

C     The following is fine as i has been declared..
      i = 1

      end