Active Debugger is an ITS that is deigned to teach C++comprehension skills based on constraint-based methodology.Students are asked to explain the changes that take place in the memory for a given C++program.Students have the freedom to ask for feedback at any point in the program.When the feedback is requested,the correct solution is dynamically generated until the line of code that a student has attempted.This solution is used to evaluate the student attempt together with the constraint-base.This generated-solution can also be viewed as a simulation to understand the changes that occur in memory after each line of code.An initial study was conducted to evaluate the effectiveness of the system in learning C++comprehension.This study involved authentic students in a computer science undergraduate course.Results revealed a positive trend towards learning.Further evaluations needs to be carried out to evaluate the effectiveness of the system.