Many Fortran programs were developed on systems that provided automatic initialization of all, or some, variables and arrays to zero. As a result, many of these programs depend, sometimes inadvertently, on this behavior, though to do so violates the Fortran standards.
You can ask g77 for this behavior by specifying the
`-finit-local-zero' option when compiling Fortran code.
(You might want to specify `-fno-automatic' as well,
to avoid code-size inflation for non-optimized compilations.)
Note that a program that works better when compiled with the
`-finit-local-zero' option
is almost certainly depending on a particular system's,
or compiler's, tendency to initialize some variables to zero.
It might be worthwhile finding such cases and fixing them,
using techniques such as compiling with the `-O -Wuninitialized'
options using g77.
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