Is there something which we can do in c but not in c++
Why is preincrement operator faster than post increment operator
Almost nothing can be done in C which is not possible in C++. There are some formatting changes in C++ that doesn't let C programs compile in C++ compilers. There is a C macro that let compiler thread that code using C compiler.
Do you mean ++i executes faster than i++? I don't agree, except by fast you mean something else. Preincrement increments the variable before using its value.