Download and use the plugin NppAutoIndent in Notepad++.In your Notepad++:
Plugins -> Plugin manager -> Available -> NppAutoIndent
NppAutoIndent plugin has 'smart' indentation for C-style languages, such as C/C++, PHP, Java and such.
It's the first release so don't expect it to be flawless, and of course it might not be completely to your preferences ;)
There is NO support for HTML/XML and such, maybe later, tag matching is much more difficult to implement.
To use it select your code and:
TextFX -> TextFX Edit -> Reindent C++ code
If you can not see
TextFX in your menu,you can install it's plug in(from here) and probably you can see
TextFX Edit -> Reindent C++ code in it,after installing.You can see more details in these pages:
Reindenting C Source Code Files With Notepad++