I'm looking for the a++ compiler too. Even the init_hls.sh in the "16.1/hls" folder expect this a++ binary. I searched for it, but there is not such binary in the whole quartus installation.
And there is no much documentation about it (Or I'm searching wrong). I found this link:
https://www.altera.com/products/design-software/high-level-design/intel-hls-compiler/overview.html.
I believe the a++ compiler is only available as beta version right now.
Currently I try to evaluate HLS tools or let's say the possibilities doing High Level design. And I must say that the Vivado HLS looks very good (good tutorial, documentation and it works). I hope that Intel/Altera could do better. Maybe some people in this forum know more.