CodeLab is the web-based interactive programming exercise system for intro programming classes in Python, Java, C++, C, and C#. It is a proven system that has been used in over 400 institutions in 20 countries and analyzed over 136,000,000 (one hundred thirty-six million) exercise submissions from more than 300,000 students.
CodeLab has 800+ short exercises, each focused on a particular programming idea or language construct. The student types in code and the system immediately judges its correctness, offering hints when the submission is incorrect. Through this process, the student gains mastery over the semantics, syntax and common usage of the language elements.