get cosy with compiler flags

The compiler flags are your friends.

I say that from experience, having just integrated some sweet tracing libraries into our make environment and by chance activating advanced type checking for our FORTRAN compiles, all 100,000 lines of them.

All sorts of mismatches started appearing in the compilation logs. Applications that had been compiled, linked and used for the last 23 years now showed mismatches in the types being passes in subroutine calls. Some harmless, but others quite ready to stab you in the back on the day that you decided that wearing chainmail shirts to work was so old fashioned.

How about these:

Missing a required subroutine argument or supplying extra arguments.
Passing zero as an integer to a routine expecting a real.
Returning a real to the calling subroutine when an integer was expected.
Passing a real array but then treating the elements as if they were double precision.
Expecting no loss in precision when combining reals and double precision numbers.
Generally finding that multiple calls to the same subroutine are not consistent.
Misuses of global common modules by concurrent equivalencing using inconsistent types.

All of this revealed by a simple compiler flag.

Get to know the flags that are available, not just for your FORTRAN compiles, but for any language. While it is true that activating one will likely increase the volume of output when you compile, it can save you from decades of thinking that the code is type consistent.

Better to curse your compiles than to have someone cursing your attention to detail a couple of decades down the track.