add implicit none to example programs that do not have it

[gareth-nx]

This adds implicit none to a number of programs in the example folder that otherwise don't have it.

While not essential, the programs are used in library documentation, and IMO it's better to demonstrate good practice.

I have run the tests using cmake --build build --target test and they all appear to pass.

[jvdp1]

Thank you @gareth-nx . I agree that it is better to demonstrate good practice.
I wonder if it might be even better to use implicit none (type, external) rather implicit none. Or would it exclude too many compilers that do not support this more recent feature?

[gareth-nx]

Thanks for the review @jvdp1.

I actually haven't moved to using implicit none(type, external) in my own programs.

From this link I understand that the main difference relates to external functions and subroutines.

In the context of the example programs, these are probably moot points. But so was the absence of implicit none, as it turned out.

The bigger question is whether we should uniformly encourage implicit none (type, external) as the default, rather than just implicit none.

I'm not sure. But maybe if there are doubts about compiler support, we can just leave it for now?

[jvdp1]

I'm not sure. But maybe if there are doubts about compiler support, we can just leave it for now?

OK. We can leave it as it is now.

[gareth-nx]

No worries. I'll wait a while in case there are other suggestions. But likely this can be merged as is.