CodeLab provides hundreds of class-tested, instructor-vetted coding exercises for students in introductory programming courses. Each exercise involves writing a small portion of a program, and focuses on a particular language construct or programming idea. In each topic, CodeLab starts by offering a very simple problem, followed by ones of increased complexity and sophistication. By giving the students immediate evaluation on their code’s correctness and offering hints on incorrect submissions, the service provides a venue where students can practice their way...