I want to add a tag like C++ in Emacs Org Mode file, but Org Mode doesn’t let me to do it. I find the explanation about tags in Org Mode:

Tags are normal words containing letters, numbers, ‘_’, and ‘@’.

So, if you want to add tags with characters besides letters, numbers, ‘_’, and ‘@’, it seems that the only way is to change the tags into other words.

I use cpp or CPlusPlus to replace C++ in the tag position in my own Org Mode file.