If you have the time then why not? C++ still widely used.

Is the C++ a suit that's been hanging in your closet for a year or several and you haven't had occasion to wear it?

After answering that question, what do you have to do to maintain the suit, and how much space would it free up if you gave it to goodwill?

I would say just work on refining your PHP/HTML skills. As an online programmer, I don't think C++ will bring you too much benefit

I really don't understand what you mean by "maintain" C++ skills. If you know C++ already then it's great. You will notice that along the way, you will be able to import most of what you learned on C++ to any "web" languages. PHP, Java, C#, C++ share a common-style syntax.

Since you already know C++, i suggest that you take a look on C# as it's more inclined to web rather than C++.

unless you are building a new browser or low level plugin (or even embedded code) I would say No. who wants to do memory management for higher level solutions.... and if you do use visual C++ you are better off with the more popular languages in .Net.

Am I right to think that in order to use C#, I will have equally to use asp?

only if you will do web programming.

C# is only a language.

.Net is a framework or platform that you use... for example to do calculations or edit files. you'll be accessing these functionatlities via C#

ASP.net is a webtechnology on top of .Net. this webtechnology allows you to programmatically communicate with the client.

Most of the time, first time web programmers in .Net use all three at once, without distinguishing.

hope this helps.