<disclaimer>I have not programmed in C/C++ for a long time (about a decade now) so this information may be out of date.</disclaimer>

The below is not commentary on the language constructs or language syntax.

C is not object oriented. There is no implicit "this" object. That's one of the best features of C++. The ability to group instance variables - i.e. member variables. Instantiating an object allows multiple instances with their own context. You can, of course, achieve the same thing in C by passing a struct (pointer) around. C++ also implicitly supports polymorphism and inheritance. You can implement these in C but why bother when the C++ compiler does this natively in the language. The C++ compiler is also much more type safe. Standard C typecasting is inherently dangerous. C++ typecasting is much safer (with the exception of reinterpret_cast which is essentially a C typecast).

C also does not have overloading. Another useful feature to make code more readable.

C# also has one big fundamental difference from C/C++. It requires a supporting runtime (the CLR). C/C++ compiles to native instructions of the target platform and interfaces with facilities provided by the operating system. C# compiles to intermediate language (IL) and the runtime interfaces with facilities provided by the operating system. The IL is translated to native instructions by a JIT (just in time) compiler. I assume it is possible to produce a binary that is pre-compiled to native instructions but that binary still requires the runtime. The C# runtime also provides garbage collection and takes care of memory management. With C/C++ you are on your own. Leak memory (or address space) all you want.

Gosh that brings back memories of years spent in a development environment and debuggers.