Error: ‘for’ loop initial declarations are only allowed in C99 or C11 mode

[Martin Frezman]

and in the documentation:

*WHICH* documentation? Which OS/version-of-gcc did you get that from?

Sorry, "man gcc"

Raspbian stretch / the default compiler (gcc 6.3)

Right. No one doubts that in Stench they (finally!) upgraded to a more-or-less current version of GCC. The discussion has been about whether or not it worked in the default version of GCC found in Jessie. To which the answer is "No".

And, given poster's latest post, it seems clear that he was using C++ all along...

[Martin Frezman]

well, ok, I'm a beginner to C, I didn't know there is a difference between gcc and g++ compiler calls

Yes. There is also a difference between C and Fortran.

[Stiller]

yes, but C is a subset of C++, and Fortran isn't

[Paeryn]

yes, but C is a subset of C++, and Fortran isn't

No, C is not a subset of C++, they share a large part but you can write perfectly valid C that won't compile in C++ without changes or which behaves differently.

[jahboater]

Yes, there is the "restrict" keyword which isn't supported in C++, the annoying casts needed when converting from a void* ......

I believe part of the rationale behind C99 and C11 was to bring C back to being a subset of C++ as it was in the old days (C++ was originally called "C with Classes"). C99 especially, had lots of good stuff from C++ included.

From Mr Stroustrup (The C++ Programming Language Fourth Edition - end of page 1271):
"Well-written C programs tend to be C++ programs as well."