I'm surprised that everyone in this question claims that std::cout is way better than printf, even if the question just asked for differences. Now, there is a difference - std::cout is C++, and printf is C (however, you can use it in C++, just like almost anything else from C). Now, I'll be honest here; both printf and std::cout have their advantages.

Real differences

Extensibility

std::cout is extensible. I know that people will say that printf is extensible too, but such extension is not mentioned in the C standard (so you would have to use non-standard features - but not even common non-standard feature exists), and such extensions are one letter (so it's easy to conflict with an already-existing format).

Unlike printf, std::cout depends completely on operator overloading, so there is no issue with custom formats - all you do is define a subroutine taking std::ostream as the first argument and your type as second. As such, there are no namespace problems - as long you have a class (which isn't limited to one character), you can have working std::ostream overloading for it.

However, I doubt that many people would want to extend ostream (to be honest, I rarely saw such extensions, even if they are easy to make). However, it's here if you need it.