I've never used C#, but have used C and C++ quite a bit and have been taught both in college. I believe that C# is simply C++, but more accurate as an Object Oriented Language (but I could EASILY be wrong about C#).
There is a LOT more code out there done in C. If you learn C++, you WILL NOT understand many of the commands used in C (this is particularly important if you're researching 'security documents'). It wouldn't take long to learn these differences, but C is a MUCH better place to learn in my opinion - It will teach you details about coding that many languages 'hide' these days. Once you understand how to use C, just start learning about Object Oriented Programming, and search for topics like 'the differences between C and C++'. Particularly the difference between the output - and how to access the class information - Although any reasonable C++ book WILL explain these differences for you.
However, this is if you want to learn how to develop software, if you're more interested in learning web design then I would suggest forgetting about C for now and just focus on PHP and MySQL...

It's ridiculous how closely related PHP is to C/C++ and what you can do with PHP is amazing, it's probably the STRONGEST scripting language I've ever used, WAY more useful then other scripting languages like javascript and VBScript (although javascript will ALWAYS be useful I think). And even comparable to full fledged languages like C/C++.
I haven't even used C/C++ since college, when developing software I actually use Delphi (which I learned after college, but I certainly wouldn't recommend Delphi as a starter language - If you really want to understand Delphi for application design, then I would suggest fully understanding C++, then migrate to Delphi. There are some major differences between the two (especially the layout of the code, how the classes work, releasing memory, etc...) but having knowledge of C++ will allow you to migrate to Delphi much easier. You can also just as easily move from PHP to Dephi as well instead of using C++ as a stepping block. Delphi is more comparable to Visual Basic I think, but WITHOUT all the nonsense and ridiculous issues that arise with VB, and MUCH more powerful.
But please, remember - MOST of the code examples you'll find even today (related to security anyways...) - Are likely done in C/C++ - mostly because most of them are used in Unix/Linux and compiled @ the command line using SSH/Telnet or run as a script through PHP/CGI/Perl etc...
If I were new to programming, I would certainly begin by learning PHP/Mysql then Delphi. This will immediately allow you to develop applications as well as web software. Once I had a good understanding of these languages, I would learn C for 'code accessibility reasons', then finally migrating to .NET (simply because it obviously isn't going away and EVERYONE seems to be using it these days - governments/large companies, etc...). It's so widely used because you can convert software from one language to another quite easily with it. I don't like it because it works a lot like java...

I hate anything that requires you to download a library package to the client. It's an annoyance, and will prevent many people from even TRYING your application...

Which is why I still haven't picked up a book on .NET myself...

Delphi is a VERY popular language, even today - And you can get paid quite a bit for knowing it because there are so few of us who actually use it today. It's a language used quite often in the industry due to it's ease of use and because there is TONS of freely distributed example code/packages available for it to do some REALLY cool and advanced applications. It is also a major cash cow without even developing software because you can easily develop your own packages that will integrate with the IDE which other programmers will gladly pay you for if it's done well.