C++ take a letter from a file

I'm working on a C++ file. And this is what I've got: The user has to type the name of a file, e.g. file1.txt, and I have to count the letters in that file. All of this is working but: after "x" letters, I have to take the next letter and show it on the screen. I don't really know how to do this?

I think it has to be an if-statement and it has to start like this: if (count_letters = x){ } But I'm really lost after that.

Thanks !