Program Visualization: An exploration of graph based visualizations to assist in student learning and programmatic evaluation

As computer science students develop more complex programs at the end of their first year of course work, comprehending the complex and varied interactions of program execution, potential control flow and data relationships become more and more difficult. Additionally, for instructors when evaluating student\u27s programs, a simplified view of more complex (longer) programs is desirable. This thesis explores algorithms to create a tool for students that provides a simplified view of these concepts via visualization. The tool created for this thesis provides interactive visual representations of student programs. This allows for a simplified representation of the entire program along with depth exploration options to examine potential control flow and data access/mutations. The following is an exploration of program visualization, with a focus on usability in an educational setting. Two main approaches will be discussed. The first attempts to visualize the call graph of a running program by showing what methods call what other methods, and the frequency in which they are invoked. The second shows all potential paths through a non-running program, by viewing the program on a per-method level. This approach also includes information about how methods interact with data. As a test case this thesis focuses on a spell check program which builds a binary search tree dictionary then searches it for input strings and provides correction suggestions if the input is not found in the dictionary. We present an evaluation of our tool via creating visualizations of four different student implementations of this program. These visualizations are then analyzed by computer science faculty to identify common threads throughout all submissions, as well as areas where individual students struggled or excelled. Additionally visualizations are used as a tool in a lecture instructing students about binary search trees. The students provide feedback as to the effectiveness of the visualizations and their comprehension of the material. We conclude that program visualization is a difficult task, especially when students are unused to visualizing control flow. Results indicate potential for use as both a student and instructor tool, though further research is required to identify optimal usage