The interview starts with a HR phone screen and two basic problem set that tests your problem solving and design skill. If you pass this test then there's a phone interview with other software developers. This test tend to test your understanding of C++, math, and design skill. After the phone interview is an in person interview where they would ask you about many gotcha in C++ and to write a few simple programs. Some of the topics in the interview include software design, design patterns, C++ syntax/data structure/exception/stl/templates... basically anything about C++ and programming is fair game.