!head('subscript checking')
normally the compiler does not check the validity of subscripts before
they are used as this can increase the time and size of programs.
it is often necessary to use the "--C" option to check subscripts while
a program is being debugged, as subscripting errors can cause strange 
things to happen in a program.
with the "--C" option all subscripts are checked to insure that they are
not too small or too large. if the subscript is outside of its bounds then
the appropriate message is printed.
!head('Debug option')
the compiler has an option (--D), that is useful for debugging programs.
normally, any line that begins with "d" in column 1 is treated as if it
started with a "c" (that is, its a comment). when the "--D" debug option
is used, all lines with a "d" in column 1 are treated as if the "d" where
replaced by a blank. this effectively allows for the inclusion of debugging
printouts etc.~for some compiles for testing purposes, and their removal
for production runs. 
!p it is the experience of most programmers that once debugging code has
been put into a program it will be needed again sooner or later to help
find another bug.
!head('Fortran DeBug program')
There exists a program called FDB which may be used to help debug Fortran
programs. it has features that allow the user to examine the value of
variables in a program, to set break points and to step thru a program
statment by statment. for more details see the FDB writeup.
!head('extra long source lines')
The Fortran standard specifies that the statement is confined to columns
1 thru 72 of the line (due to the format of punched cards where columns 
73 thru 80 are used for a sequence number). this is often inconvenient for
programmers entering programs thru a terminal, particularly so if any sort
of indentation scheme is used. the "--E" compiler option causes that restriction
to be removed. lines may then be arbitrarily long (up to 512 characters).
it is recommended that lines be kept somewhat shorter than 72 characters
as it allows for later modifications and transfer to other systems which
might not allow for longer lines.
!head('Continuation lines')
Naturally the compiler accepts the standard continuation of a non-blank
(and non-zero) character in column six of an input line. it also (for compatibility with Bell's  fc compiler) accepts 
an ampersand (&) in column one as an alternate continuation marker.
