iterators in C#?

Hey kids!

There is a piece of code in my C++ library that I would like to recreate in C#, that is... if C#'s String has not yet come with that solution :)

for (std::string::iterator it = str.begin(); it!=str.end(); ++it)
        if(!std::isalpha(*it,loc)) {
            //do something;
        }

Worry is a misuse of imagination :)