A Controlled Experiment to Assess the Bene ts of Procedure Argument Type

Type checking is considered an important mechanism for detecting programming errors, especially interface errors. This report describes an experiment to assess the defect-detection capabilities of static, inter-module type checking. The experiment uses Ansi C and Kernighan&Ritchie (K&R) C. The relevant di erence is that the Ansi C compiler checks module interfaces (i.e., the parameter lists of calls to external functions), whereas K&R C does not. The experiment employs a counterbalanced design in which each of the 40 subjects, most of them CS Ph.D. students, writes two non-trivial programs that interface with a complex library (Motif). Each subject writes one program in Ansi C and one in K&R C. The input to each compiler run is saved and manually analyzed for defects. Results indicate that delivered Ansi C programs contain signi cantly fewer interface defects than delivered K&R C programs. Furthermore, after subjects have gained some familiarity with the interface they are using, Ansi C programmers remove defects faster and are more productive (measured in both delivery time and functionality implemented).