You need to decide whether you are programming in C or in C++. They are not the same language. Your error message indicates to me that you have named your file "something.c", which means the compiler will compile it as C. It will not like the string class or C++ I/O (cout, cin).
If you decide to write it as C++, then you will need to change the file's extension. You will also not want to include stdio.h. There's really no reason to include it, since you aren't using an C-style I/O (printf, scanf, fgets, etc.), but if you wanted to use C-style I/O, you would include cstdio, not stdio.h. This places those functions in the standard namespace.
If you were writing anything but a trivial program, you would not want to use "using namespace standard;" That statement brings about lebenty-zillion symbols into your program. With much code at all, you're almost bound to duplicate one and cause yourself much grief.
Decide which language you're using, and try again.